Classifications

• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
  • F28G1/00—Non-rotary, e.g. reciprocated, appliances
  • F28G1/12—Fluid-propelled scrapers, bullets, or like solid bodies

Definitions

• the invention relates to an installation for steam cracking of hydrocarbons, for recycling erosive solid particles.
• the object of the invention is in particular to avoid this drawback and to recycle solid particles with means of current design, or with a long service life.
• the invention also aims to easily regulate the flow rate of solid particles recycled in the steam cracking installation, ensuring high reliability of the decoking means vis-à-vis the integrity of the equipment.
• an installation for steam cracking of hydrocarbons comprising at least one furnace. 2 for cracking hydrocarbons, an indirect quenching exchanger for the effluents leaving the furnace, and means for direct quenching of the effluents, as well as means for injecting into the furnace a low flow rate of fine solid particles and means, such as a cyclone, placed between the indirect quenching exchanger and the direct quenching means for the separation of solid particles and gaseous steam cracking effluents, characterized in that it comprises a storage tank for solid particles, of which the inlet is connected to the solids outlet of the cyclone and the outlet of which is connected to a pipe for injecting particles into the installation, means for isolating this tank, such as valves, and a source of pressurized gas connected on the one hand to the solid particle injection pipe and on the other hand to the tank by means such as a valve for increasing the internal pressure of this tank to a value at least equal that the point of injection of the particles in the 20
• the injection of solid particles into the oven during its operation is then discontinued.
• the aforementioned reservoir makes it possible to store the solid particles during the phase of non-injection of particles or of non-decoking.
• the solid particles can be brought to a sufficient pressure and easily recycled, in the form of a solid suspension in dilute phase, to the point of injection into the installation. steam cracking and without the need to use a very high speed carrier gas stream. This greatly reduces the erosion of the means for recycling solid particles.
• 35 providing the carrier gas stream also serves to increase the pressure in the storage tank solid particles. Due to the pressure balancing which is thus obtained, an overpressure liable to compact the solid particles or to cause too sudden evacuation of the particles from the tank is avoided.
• the installation comprises an intermediate tank mounted between the outlet of the cyclone and the inlet of the aforementioned tank, and means for isolating this intermediate tank, such as valves.
• the installation comprises a pipe connected as a bypass to the indirect quenching exchanger, between the outlet of the cracking furnace and the aforementioned cyclone, in order to take a small fraction of the outgoing gaseous effluent flow from the oven and to dry the solid particles by direct contact with this fraction removed, at a temperature corresponding to an almost total absence of liquid on said solid particles.
• the cracked gases leaving the indirect quench heat exchanger 1 are at a temperature generally between 350 and 600 ° C, limiting the side reactions, and yet high enough so that these gases do not contain substantially no liquid. It is however possible, when the charge to be steam cracked is heavy (diesel or heavy naphtha for example) that these gases contain a mist of very heavy hydrocarbons, or tars, or "liquid" coke.
• the invention makes it possible to vaporize or carbonize most of these liquid traces, without using known means consisting of burning these liquids in the presence of oxygen, very delicate to carry out from the point of view of safety.
• the increase in temperature of the solid particles leaving the indirect quenching exchanger is approximately 30 to 250 ⁇ C to vaporize or carbonize, as the case may be, traces of liquid.
• the steam cracking installation can therefore be used with relatively heavy loads liable to lead to traces of condensed hydrocarbons leaving the indirect quench exchanger, without it being necessary to impose a too high permanent temperature at the outlet. of this indirect quenching exchanger, which would lead to energy losses during the operation of the installation.
• the bypass can indeed only be put into service during particle injection periods.
• This simple method of drying the solid particles also prevents them from sticking during separation in the cyclone or recycling via the aforementioned tanks.
• this bypass pipe is connected to the conduit connecting the indirect quenching exchanger to the cyclone, upstream of the cyclone (possibly just at the outlet of the quenching exchanger). The fraction of the effluent flow rate taken off the furnace is then mixed with the effluent flow rate leaving the indirect quenching exchanger, before separation of the solid particles in the cyclone.
• the bypass pipe is connected to the solids exit from the cyclone and lead to a secondary cyclone at high temperature, sufficient to ensure the vaporization and / or carbonization of the traces of liquid present on the solid particles.
• the solid particles leaving the main cyclone are entrained by a small flow of gaseous effluents, which avoids their sticking before their overheating by contact with the abovementioned fraction taken from the flow of gaseous effluents leaving the oven.
• the secondary cyclone can have much smaller dimensions than that of the main cyclone and operates at a higher temperature, which allows either vaporization or carbonization of the traces of liquid present on the solid particles.
• the installation also comprises means for pre-quenching said fraction taken from the flow of gaseous effluents, these means being provided in the vicinity of the upstream end of said bypass pipe and comprising for example means for injecting dilution vapor.
• the presoaked may consist of a cooling (by direct contact with a gas) of between 70 and 200 ° C leaving the furnace effluent and collected in the bypass.
• the outputs of the indirect quenching exchangers of the ovens are connected to common means for separating and recycling solid particles, including the aforementioned cyclones and reservoirs.
• the outputs of the indirect quench exchangers are connected to the common means of separation and recycling of solid particles by bypass pipes which are provided with isolation valves and which are connected to the pipes connecting these outlets to the direct quenching means. .
• the isolation valves of these bypass pipes remain permanently in the open position. They then do not fulfill a sealing function and are, for example, simple, non-waterproof shutters.
• An installation of this type has a number of important advantages: the decoking of the various steam cracking ovens can be carried out sequentially, without the need to use large-diameter isolation valves specially designed for the passage of gas. loaded with erosive particles, which are extremely expensive, - bypass pipes through which gaseous effluents pass loaded with solid particles are never connected to the atmosphere, nor to a source of oxygen-containing gas, which is a important safety factor; - The general reliability of the installation is greatly increased by the fact that the abovementioned isolation valves remain in the open position and are in principle not operated during normal operation of the installation, unlike the known methods in which completely isolates the circuit during decoking;
• FIG. 1 is a diagrammatic representation of part of the means for recycling solid particles according to the invention, in a first state;
• FIG. 2 represents another state of these means;
• FIG. 3 represents a steam cracking installation according to the invention, allowing the drying of solid particles;
• Figure 4 shows an alternative embodiment of this installation;
• FIG. 5 represents a steam cracking installation according to the invention, of the type comprising several steam cracking ovens arranged in patallel.
• FIGS. 1 and 2 show, by way of example, part of the means for recycling solid particles according to the invention.
• These means comprise a cyclone 10, which is supplied by a heat exchanger carrying out an indirect quenching of the gaseous effluents leaving a hydrocarbon steam cracking furnace, and which comprises, in the upper part, an outlet 12 for gaseous effluents leading to direct quenching means and, in the lower part, an outlet 14 for solid particles separated from the gaseous effluents in the cyclone 10.
• the outlet 14 is connected by an isolation valve 16 to the upper inlet 18 of a tank 20 comprising means 22, such as a screen, for separating and retaining coarse solid particles, as well as an orifice 24 for discharging these particles.
• the lower part of the tank 20, in which the fine solid particles collect is connected by a motorized rotating member 26, of the rotary airlock type, screw or rotary lock, and by a valve.
• the outlet of the reservoir 30 is connected, downstream of the valve 34, to a conduit 36 for recycling solid particles in the steam cracking installation.
• a source 38 of pressurized gas supplies the conduit 36 with a gas flow at medium or relatively low speed.
• a three-way valve 40 makes it possible to connect the reservoir 30 either to the source of pressurized gas 38, or to the conduit 12 for the gas outlet from the cyclone. Stop valves 42 are provided in the conduits connecting the valve 40 to the source of pressurized gas 38 and to the conduit 12 respectively.
• An independent reservoir 44 filled with solid particles of determined average particle size allows, by means of a motorized rotating member 46 and an isolation valve 48, to inject an addition of solid particles into the recycling conduit 36
• the upper part of the reservoir 44 is connected to the outlet of this reservoir by a pressure equalization conduit 50.
• the rotating member 46 makes it possible to regulate the flow of make-up particles.
• the reservoir 20 may be provided, in the lower part, with a purge duct 52, making it possible to withdraw a certain quantity of solid particles.
• a barrier gas inlet pipe 53 opens into the upper part of the reservoir 20.
• the barrier gas is free of heavy aromatics and may be water vapor. It avoids coking of the tank 20 and the sieve 22.
• the downstream isolation valve 34 of this reservoir is open, the rotating member 32 is rotated and the internal volume of the reservoir 30 is connected to the source of pressurized gas 38 via the valve 40, the corresponding stop valve 42 being open.
• the gas delivered by the source 38 is at a pressure which is at least equal to or slightly greater than the pressure at the point of injection of the solid particles in the steam cracking installation and which is greater than the pressure in the outlet conduit 12 of the cyclone 10.
• the internal pressure of the reservoir 30 is therefore increased relative to that of the upper reservoir 20 and is in equilibrium with the pressure in the recycling conduit 36.
• the source 38 delivers in this conduit a gas flow at relatively low speed between 5 and 25 m / s, for example between 10 and 20 m / s, which makes it possible to transport the solid particles in dilute suspension up to at least one injection point in the steam cracking installation.
• the low speed of the carrier gas stream prevents significant erosion of the recycling conduit.
• the isolation valve 34 is closed and the reservoir 30 is connected to the cyclone outlet conduit 12 via the valve 40.
• the reservoir 30 is then at the same pressure as the upper reservoir 20, and it it suffices to open the isolation valve 28 and to drive the rotating member 26 so that the solid particles contained in the reservoir 20 can be transferred to the reservoir 30.
• the pressures between these two reservoirs could be equalized, not at the pressure of the cyclone 10, but at the pressure of the gas source 38, after having isolated the tank 20, and having connected it to the gas source 38
• the purge duct 52 makes it possible to remove an excess of solid particles from the tank 20, an excess consisting of a mixture of abrasive particles coming from the auxiliary tank and coke particles detached from the internal walls of the installation. steam cracking. Regular purging of the tank 20 makes it possible to avoid the accumulation of solid particles of medium size in the flow of recycled particles in the installation, and to reduce the coke concentration there.
• the make-up tank 44 makes it possible to add the desired quantity of solid particles having the desired particle size into the flow of recycled particles.
• the motorized rotating members which are interposed between the tank outlets and their downstream isolation valves, make it possible to regulate the flow of solid particles leaving the tanks and to avoid obstruction or blockage of the downstream valves.
• the reservoirs 20, 30 can be arranged in parallel and not in series. Referring now to Figure 3, in which there is shown schematically means' of drying solid particles used for decoking the installation.
• This plant comprises a steam cracking furnace, generally designated by the reference 54, the output gaseous effluent is connected to the input r of a heat exchanger 56 indirect quenching.
• the outlet of this exchanger is connected to the inlet of cyclone 10, whose gas outlet 12 is connected to the means 58 for direct quenching of the gaseous effluents, and whose solids outlet 14 is connected to the aforementioned means 20, 30 for storage solid particles.
• the invention provides a bypass pipe 60, the upstream end of which is connected to the outlet pipe of the furnace 54, upstream of the quench exchanger 56, and the downstream end of which is connected to the pipe of outlet of the quench exchanger 56 upstream of the inlet of the cyclone 10.
• This bypass pipe 60 comprises a calibrated orifice 62, making it possible to take a small fraction of the flow of gaseous effluents leaving the oven 54.
• means 64 for indirect quenching such as means for injecting a certain quantity of steam dilution.
• the gaseous effluents which leave the oven 54 at a temperature of approximately 850 ° C. are cooled to approximately 700 ° C. in the pipe 60.
• the gases leaving the indirect quench exchanger 56 are for example at a temperature of about 400 ° C and are heated by direct contact with the waste gas supplied by the bypass line 60 at a temperature for example of about 480 ° C. This rise in temperature is in principle sufficient to vaporize the traces of liquid present in the flow of gaseous effluents entering the cyclone 10.
• FIG. 4 represents an alternative embodiment of these means for drying solid particles.
• the bypass pipe 60 is connected to the solids outlet 14 of the cyclone 10 and leads to the inlet of an auxiliary cyclone 70 having dimensions considerably smaller than those of the above-mentioned cyclone 10.
• the gas outlet 72 cyclone 70 is connected to the inlet of the direct quenching means 58, by means of an ejector 74 or similar means.
• the exit of solids from auxiliary cyclone 70 leads to storage tanks 20, 30 mentioned above.
• the operation of this variant is as follows.
• a small fraction of the flow of gaseous effluents leaving the oven 54 is sampled by the bypass pipe 60 and mixed with a small flow of gaseous effluents leaving with the solid particles of the main cyclone 10, to be introduced into the auxiliary cyclone 70.
• the hot gases leaving the cyclone 70 are returned via the ejector 74 to the means 58 for direct quenching.
• the valve 66 of Figures 3 and 4 must be designed to operate at high temperature and resist the erosive particles which pass through it. This type of valve is expensive. It can be eliminated by connecting to the pipe 60, upstream from calibrated orifices 62, a conduit 75 for supplying a relatively cold barrier gas which prevents the removal of effluents from the oven, outside from decoking periods. Such a barrier gas can be taken from outlet 12 of cyclone 10 and recompressed, for example by an ejector, as shown in the drawing. This barrier gas can also be used for the pre-quenching of the gaseous effluents sampled during the decoking periods. Under these conditions, the means 64, 68 can be omitted. Finally, as shown in Figure 4, the embodiments of Figures 3 and 4 can be combined.
• FIG. 5 schematically shows a steam cracking installation according to the invention, comprising several cracking ovens arranged in parallel.
• This installation is of the sequential decoking type of cracking ovens and comprises conduits 36 for injecting solid particles connecting the aforementioned storage means 20, 30 to the points of injection of particles into the ovens 54, each of these conduits 36 comprising a small shut-off valve 78 immediately upstream from the point of injection into each furnace 54.
• the outputs of the indirect quenching exchangers 56 are moreover connected, by bypass pipes 80 comprising isolation valves 82, to common means for separating solid particles comprising at least one cyclone 10 of the aforementioned type.
• the solids outlet 14 of this cyclone is connected to the aforementioned storage means 20, 30, and the gas outlet 12 of the cyclone is connected, with the conduits 76, to the inlet of the direct quenching means 58.
• conduits 76 include isolation valves 84, provided downstream of the branching of the branch pipes 80.
• This installation can be used in the following manner: When the decoking of a cracking oven has to be carried out, for example that of the oven 54 l the isolation valve 84 of its conduit 76 is closed while the valve 82 of the corresponding bypass pipe 80 is open. The injection of solid particles into the oven 54-L is carried out by opening the corresponding stop valve 78.
• valves 84 of the conduits 76 of the other ovens are open, and the valves 82 of the bypass pipes 80 of these other ovens are closed, so that the flow of gaseous effluents and solid particles leaving the oven 54 x passes through the cyclone 10, while the flow rates of gaseous effluents leaving the other ovens directly reach the means 58 for direct quenching.
• the corresponding valve 78 is closed, the valve 84 is opened and the valve 82 associated with this oven is closed, then the operations already described for the oven 54 2 are repeated. decoking the oven 54 x . -
• valves 82 of the bypass lines 80 are operated relatively frequently.
• these valves are extremely expensive, since they are designed to be traversed by large flows of gas charged with erosive particles. It is therefore preferable to operate this installation as follows: all the valves 82 are left open at all times.
• the associated valve 84 is closed and an injection of erosive solid particles is carried out in this oven, by opening the corresponding valve 78.
• the valves 84 associated with the other ovens are open, as are the valves 82 of the corresponding bypass pipes.
• valves 82 remain permanently in the open position.
• valves 82 it is possible to use much less expensive valves than in the previous case, for example non-watertight means such as shutters, to regulate the flow rates of gaseous effluents which pass through the pipes 80, during the periods of decoking and outside these periods.
• the invention also applies to the sequential decoking of different passes of the same oven opening into indirect quench exchangers, the outlets of which are connected by branches to common means of separation and recycling of solid particles.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Thermal Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Organic Chemistry (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Cyclones (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Fertilizers (AREA)

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• 1989
  • 1989-10-06 FR FR8913070A patent/FR2652817B1/fr not_active Expired - Fee Related
• 1990
  • 1990-10-05 AT AT90914930T patent/ATE109195T1/de active
  • 1990-10-05 EP EP90914930A patent/EP0447527B1/de not_active Expired - Lifetime
  • 1990-10-05 JP JP2513930A patent/JP2898091B2/ja not_active Expired - Lifetime
  • 1990-10-05 WO PCT/FR1990/000711 patent/WO1991005031A1/fr not_active Ceased
  • 1990-10-05 US US07/700,196 patent/US5183642A/en not_active Expired - Fee Related
  • 1990-10-05 ES ES90914930T patent/ES2063376T3/es not_active Expired - Lifetime
  • 1990-10-05 DE DE69011084T patent/DE69011084T2/de not_active Expired - Fee Related
  • 1990-10-05 DK DK90914930.4T patent/DK0447527T3/da active

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