WO2011122329A1 - 炭化水素の製造方法 - Google Patents
炭化水素の製造方法 Download PDFInfo
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- WO2011122329A1 WO2011122329A1 PCT/JP2011/056032 JP2011056032W WO2011122329A1 WO 2011122329 A1 WO2011122329 A1 WO 2011122329A1 JP 2011056032 W JP2011056032 W JP 2011056032W WO 2011122329 A1 WO2011122329 A1 WO 2011122329A1
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- hydrocarbon oil
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- light hydrocarbon
- reaction
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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
- C10G2/00—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon
- C10G2/30—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen
- C10G2/32—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts
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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
- C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
- C10G2300/10—Feedstock materials
- C10G2300/1022—Fischer-Tropsch products
Definitions
- the present invention relates to a hydrocarbon production method in which hydrocarbons are synthesized from hydrogen gas and carbon monoxide gas in the presence of a catalyst, and the resulting hydrocarbons are fractionated.
- synthesis gas mainly composed of carbon monoxide gas (CO) and hydrogen gas (H 2 ) is used.
- a method using a Fischer-Tropsch synthesis reaction (hereinafter sometimes referred to as “FT synthesis reaction”) as a source gas is known.
- FT synthesis reaction a Fischer-Tropsch synthesis reaction
- As a synthesis reaction system for synthesizing hydrocarbons by an FT synthesis reaction for example, a bubble column type slurry in which a synthesis gas is blown into a slurry in which catalyst particles are suspended in a liquid hydrocarbon in a reactor to perform an FT synthesis reaction A bed FT synthesis reaction system is disclosed (Patent Document 1).
- a liquid phase composed of a liquid reaction product and unreacted synthesis gas (hydrogen gas and carbon monoxide gas).
- Gas-liquid separation into a gas phase containing This gas-liquid separation step is generally performed at a relatively high temperature at which the wax fraction contained in the reaction product maintains fluidity.
- the FT synthesis reaction product is contained in the gas phase.
- light hydrocarbons having a relatively low boiling point are included.
- the liquid phase is composed of heavy hydrocarbon oil having a relatively high boiling point.
- the separated gas phase is then cooled, and again into a liquid hydrocarbon (light hydrocarbon oil) and a gas mainly containing gaseous hydrocarbons (approximately 4 or less carbon atoms) and unreacted synthesis gas at room temperature. Gas-liquid separation.
- the light hydrocarbon oil and heavy hydrocarbon oil are extracted from each buffer tank, mixed, For example, it is supplied to a rectification column having a multi-stage tray.
- a mixed oil of light hydrocarbon oil and heavy hydrocarbon oil is, for example, a naphtha fraction extracted from the top of the rectifying column or an intermediate fraction extracted from the center of the rectifying column. And fractionated into a wax fraction extracted from the bottom of the rectifying column.
- Each of the obtained fractions becomes various fuel base materials through an upgrading process, which is a process for performing hydrogenation and fractionation.
- the reaction temperature may be temporarily deviated from the set value, or the slurry liquid level may be temporarily changed. is there.
- the deviation from the set value of the temporary reaction temperature or the fluctuation of the slurry liquid level in the FT synthesis reaction affects the inflow amounts of light hydrocarbon oil and heavy hydrocarbon oil into the buffer tanks.
- each buffer tank is designed so that the liquid level of each buffer tank is constant even if the inflow amounts of light hydrocarbon oil and heavy hydrocarbon oil to each buffer tank vary. The extraction flow rates of light hydrocarbon oil and heavy hydrocarbon oil from each were adjusted.
- the ratio between the light hydrocarbon oil and the heavy hydrocarbon oil supplied to the rectification column and the total flow rate are likely to vary.
- the distillation cut of each fraction in the rectification column is kept constant, that is, the extraction tray tray temperature of each fraction of the rectification column is kept constant. Need to keep on.
- the ratio of light hydrocarbon oil to heavy hydrocarbon oil at the rectifying column inlet varies, keep the extraction tray temperature constant by changing the extraction amount of each fraction from the rectifying column.
- This invention is made
- the present inventor replaces the conventional method of controlling the liquid level height of each buffer tank for temporarily storing the light hydrocarbon oil and the heavy hydrocarbon oil with a constant level, instead of the light carbon oil from each buffer tank.
- the above temporary The present invention has been completed by conceiving that stable mixed oil can be supplied to the rectification column by eliminating the influence of various fluctuations.
- the hydrocarbon production method of the present invention comprises a synthesis step of synthesizing hydrocarbons by a Fischer-Tropsch synthesis reaction from continuously supplied hydrogen gas and carbon monoxide gas in the presence of a catalyst, and gas-liquid separation.
- Gas-liquid separation step of separating the hydrocarbon into light hydrocarbon and heavy hydrocarbon oil, and the light hydrocarbon oil obtained from the light hydrocarbon and the heavy hydrocarbon oil, respectively, in each buffer tank Continuously supplying a temporary storage step, and continuously extracting the light hydrocarbon oil and heavy hydrocarbon oil from the buffer tanks, mixing the light hydrocarbon oil and heavy hydrocarbon oil, and performing rectification.
- the respective estimated production rates of the light hydrocarbon oil and the heavy hydrocarbon oil are determined based on the set reaction temperature in the synthesis step, and the light hydrocarbon oil in the extraction step and The extraction flow rate of the heavy hydrocarbon oil is controlled to be equal to the respective estimated production rates.
- the synthesis step and the gas-liquid separation step may be performed in a slurry bed reactor having a gas phase portion at the top.
- the estimated production rates of the light hydrocarbon oil and the heavy hydrocarbon oil may be determined based on the relationship between the reaction temperature of the Fischer-Tropsch synthesis reaction and the chain growth probability regarding the catalyst used in the synthesis step. .
- a rectifying column when a deviation from a temporary set value of reaction temperature in an FT synthesis reaction or a change in slurry liquid level in a slurry bed reactor occurs.
- the fluctuation of the ratio of the light hydrocarbon oil to the heavy hydrocarbon oil and the total flow rate supplied to the column can be suppressed, and the operation of the rectifying column is stabilized.
- FIG. 1 shows an example of a liquid fuel production system.
- the liquid fuel production system 1 includes a synthesis gas production unit 3, an FT synthesis unit 5, and an upgrading unit 7.
- a natural gas that is a hydrocarbon raw material is reformed to produce a synthesis gas containing carbon monoxide gas and hydrogen gas.
- the FT synthesis unit 5 hydrocarbons are synthesized from the synthesis gas produced in the synthesis gas production unit 3 by an FT synthesis reaction.
- a bubble column type slurry bed FT synthesis reactor is used as the FT synthesis reactor.
- the upgrading unit 7 the hydrocarbon synthesized in the FT synthesis unit 5 is hydrotreated and fractionated to produce a liquid fuel (naphtha, kerosene, light oil) base material, wax, and the like.
- the synthesis gas production unit 3 mainly includes a desulfurization device 10, a reformer 12, an exhaust heat boiler 14, gas-liquid separators 16 and 18, a decarbonation device 20, and a hydrogen separation device 26.
- the desulfurization apparatus 10 includes a hydrodesulfurization reactor and the like, and removes sulfur compounds from natural gas as a raw material.
- the natural gas supplied from the desulfurization apparatus 10 is reformed by, for example, a steam / carbon dioxide reforming method, and contains carbon monoxide gas (CO) and hydrogen gas (H 2 ) as main components.
- a synthesis gas containing is produced.
- the exhaust heat boiler 14 the exhaust heat of the synthesis gas produced in the reformer 12 is recovered, and high-pressure steam is obtained.
- the gas-liquid separator 16 water heated by heat exchange with the high-temperature synthesis gas in the exhaust heat boiler 14 is separated into gas (high-pressure steam) and liquid water.
- the condensed component is removed from the synthesis gas cooled by the exhaust heat boiler 14, and the gaseous component is supplied to the decarbonation device 20.
- the decarbonator 20 absorbs and removes carbon dioxide from the synthesis gas supplied from the gas-liquid separator 18 using the absorbent, and regenerates by removing the carbon dioxide from the absorbent containing the carbon dioxide. And a regeneration tower 24.
- the hydrogen separator 26 a part of the hydrogen gas contained in the synthesis gas is separated from the synthesis gas from which the carbon dioxide gas has been separated by the decarbonation device 20.
- the FT synthesis unit 5 mainly includes an FT synthesis reactor 30, which is a bubble column type slurry bed reactor, a gas-liquid separator 34, a catalyst separator 36, a gas-liquid separator 38, and a first rectifying tower 40.
- the FT synthesis reactor 30 is a reactor that synthesizes liquid hydrocarbons from synthesis gas by an FT synthesis reaction, and mainly includes a reactor main body 80 and a cooling pipe 81.
- the reactor main body 80 is a substantially cylindrical metal container in which a slurry in which solid catalyst particles are suspended in liquid hydrocarbon (the product of the FT synthesis reaction) is accommodated. Yes.
- a synthesis gas mainly composed of carbon monoxide gas and hydrogen gas is injected into the slurry.
- the synthesis gas blown into the slurry becomes bubbles and rises from the lower side of the reactor main body 80 in the height direction (vertical direction) to the upper side.
- the synthesis gas dissolves in the liquid hydrocarbon, and comes into contact with the catalyst particles, whereby the synthesis of the hydrocarbon (FT synthesis reaction) proceeds.
- the synthesis gas rises as bubbles in the reactor main body 80, an upward flow of slurry (air lift) is generated in the reactor main body 80. Thereby, a circulating flow of slurry is generated inside the reactor main body 80.
- the unreacted synthesis gas that has risen up to the top of the reactor main body 80 and the hydrocarbons generated by the FT synthesis reaction under the conditions in the reactor main body 80 are extracted from the top of the reactor main body 80.
- hydrocarbons that are gases under the conditions in the reactor main body 80 are referred to as “light hydrocarbons”.
- the water heated through the cooling pipe 81 disposed in the FT synthesis reactor 30 is separated into water vapor (medium pressure steam) and liquid water. Unreacted synthesis gas and light hydrocarbons extracted from the top of the FT synthesis reactor 30 are introduced into the gas-liquid separator 38 and cooled.
- the liquid component condensed by cooling is separated from the unreacted synthesis gas and the gaseous component mainly composed of hydrocarbon gas having 4 or less carbon atoms.
- this liquid component is referred to as “light hydrocarbon oil”.
- the light hydrocarbon oil is mainly composed of hydrocarbons corresponding to a naphtha fraction and a middle fraction.
- the catalyst separator 36 the slurry extracted from the central portion of the FT synthesis reactor 30 is separated into a catalyst and a liquid hydrocarbon product.
- the liquid hydrocarbon product obtained by the gas-liquid separator 36 is referred to as “heavy hydrocarbon oil”.
- the heavy hydrocarbon oil is composed of a hydrocarbon heavier than a light hydrocarbon.
- the heavy hydrocarbon oil supplied from the FT synthesis reactor 30 via the catalyst separator 36 and the light hydrocarbon oil supplied via the gas-liquid separator 38 are mixed.
- the mixed oil thus obtained is fractionated and separated into fractions (naphtha fraction, middle fraction, wax fraction) according to the boiling point.
- the naphtha fraction is a fraction having a boiling point lower than about 150 ° C.
- the middle fraction is a fraction having a boiling point of about 150 to 360 ° C.
- the wax fraction is a fraction having a boiling point higher than about 360 ° C.
- the FT synthesis unit 5 includes a first buffer tank 91 in which the light hydrocarbon oil extracted from the gas-liquid separator 38 is temporarily stored, and a heavy hydrocarbon oil extracted from the catalyst separator 36. Is further provided with a second buffer tank 92 in which is temporarily stored, and a heater 93 that heats the mixed oil supplied to the first fractionator 40. A second flow rate adjusting valve 97 is attached to the pipe 96 connecting the second buffer tank 92 and the heater 93, and a first flow rate adjusting valve is connected to the pipe 94 connecting the first buffer tank 91 and the pipe 96. 95 is attached.
- the FT synthesis unit 5 receives a reaction temperature set value of the FT synthesis reaction, and has a control unit 98 that adjusts the valve openings of the first flow rate adjustment valve 95 and the second flow rate adjustment valve 97 based on the temperature information.
- the first buffer tank 91 and the second buffer tank 92 are provided with level meters 91a and 92a for measuring the liquid level height. As the level meters 91a and 92a, for example, magnet type level meters are used.
- the upgrading unit 7 includes a wax fraction hydrocracking reactor 50, a middle fraction hydrotreating reactor 52, a naphtha fraction hydrotreating reactor 54, gas-liquid separators 56, 58 and 60, and a second rectification.
- a tower 70 and a naphtha stabilizer 72 are mainly provided.
- the wax fraction hydrocracking reactor 50 is connected to the bottom of the first rectifying column 40 to supply the wax fraction.
- the middle distillate hydrotreating reactor 52 is connected to the center of the first rectifying column 40 so that the middle distillate is supplied.
- the naphtha fraction hydrotreating reactor 54 is connected to the top of the first rectifying column 40 to supply the naphtha fraction.
- Gas-liquid separators 56, 58, and 60 are provided corresponding to the reactors 50, 52, and 54, respectively.
- the liquid hydrocarbons supplied from the gas-liquid separators 56 and 58 are fractionated according to the boiling point.
- the naphtha stabilizer 72 liquid hydrocarbons contained in the naphtha fraction supplied from the gas-liquid separator 60 and the second rectifying tower 70 are fractionated, and a gas component having 4 or less carbon atoms is discharged as flare gas, Components having 5 or more carbon atoms are recovered as naphtha of the product.
- the desulfurization apparatus 10 includes a hydrodesulfurization reactor and a subsequent hydrogen sulfide adsorption apparatus.
- a hydrodesulfurization reactor filled with a known hydrodesulfurization catalyst, sulfur compounds in natural gas are hydrogenated and converted to hydrogen sulfide. This hydrogen sulfide is adsorbed and removed by a hydrogen sulfide adsorbing device disposed in the subsequent stage.
- Natural gas (which may contain carbon dioxide gas) desulfurized in this way is generated in carbon dioxide gas (carbon dioxide gas) supplied from a carbon dioxide supply source (not shown) and in the exhaust heat boiler 14. After the steam is mixed, the reformer 12 is supplied. In the reformer 12, the natural gas is reformed by using steam / carbon dioxide reforming method, for example, by using steam and carbon dioxide, and a high temperature mainly composed of carbon monoxide gas and hydrogen gas. Generate synthesis gas.
- the fuel gas and air for the burner included in the reformer 12 are supplied to the reformer 12, and by the combustion heat of the fuel gas in the burner and the radiant heat in the furnace of the reformer 12, Reaction heat necessary for the steam / carbon dioxide reforming reaction, which is an endothermic reaction, is provided.
- the high-temperature synthesis gas (for example, 900 ° C., 2.0 MPaG) produced in the reformer 12 in this way is supplied to the exhaust heat boiler 14 and exchanges heat with water flowing through the exhaust heat boiler 14. Is cooled (for example, 400 ° C.), and exhaust heat is recovered. At this time, the water heated by the synthesis gas in the exhaust heat boiler 14 is supplied to the gas-liquid separator 16, and the gas component from the gas-liquid separator 16 is reformed as high-pressure steam (for example, 3.4 to 10.0 MPaG). The water in the liquid is returned to the exhaust heat boiler 14 after being supplied to the vessel 12 or other external device.
- high-temperature synthesis gas for example, 900 ° C., 2.0 MPaG
- the synthesis gas cooled in the exhaust heat boiler 14 is supplied to the absorption tower 22 of the decarboxylation device 20 or the FT synthesis reactor 30 after the condensate is separated and removed in the gas-liquid separator 18. .
- the carbon dioxide gas contained in the synthesis gas is absorbed by the stored absorption liquid, and the carbon dioxide gas is removed from the synthesis gas.
- the absorption liquid containing carbon dioxide gas in the absorption tower 22 is introduced into the regeneration tower 24, and is heated by, for example, steam and stripped.
- the carbon dioxide gas removed from the absorption liquid is transferred from the regeneration tower 24 to the reformer 12. To be reused for the reforming reaction.
- the synthesis gas produced by the synthesis gas production unit 3 is continuously supplied to the FT synthesis reactor 30 of the FT synthesis unit 5.
- the synthesis gas supplied to the FT synthesis reactor 30 is compressed at an appropriate pressure for the FT synthesis reaction by a compressor (not shown) provided in a pipe connecting the decarboxylation device 20 and the FT synthesis reactor 30.
- the pressure is increased to (for example, 3.6 MPaG).
- the compressor may not be provided.
- a part of the synthesis gas from which the carbon dioxide gas is separated by the decarboxylation device 20 is also supplied to the hydrogen separation device 26.
- the hydrogen separator 26 a part of hydrogen gas contained in the synthesis gas is separated by a hydrogen PSA (pressure (swing adsorption) method.
- the separated hydrogen gas is subjected to various hydrogen utilization reactions in which a predetermined reaction is performed using hydrogen gas in the liquid fuel production system 1 from a gas holder (not shown) or the like via a compressor (not shown).
- Continuously supplied to the apparatus for example, hydrodesulfurization reactor of the desulfurization apparatus 10, wax fraction hydrocracking reactor 50, middle fraction hydrotreating reactor 52, naphtha fraction hydrotreating reactor 54, etc. Is done.
- the FT synthesis unit 5 synthesizes hydrocarbons from the synthesis gas produced by the synthesis gas production unit 3 by an FT synthesis reaction.
- the hydrocarbon synthesis method will be described.
- the synthesis gas produced in the synthesis gas production unit 3 flows from the bottom of the reactor main body 80 constituting the FT synthesis reactor 30 and passes through the slurry stored in the reactor main body 80. To rise. At this time, in the reactor main body 80, the carbon monoxide gas and hydrogen gas contained in the synthesis gas react with each other by the above-described FT synthesis reaction to generate hydrocarbons. Further, during this synthesis reaction, water is circulated in the cooling pipe 81, the reaction heat of the FT synthesis reaction is removed, and the water heated by this heat exchange is vaporized to become steam. As for this water vapor, the water liquefied in the gas-liquid separator 34 is returned to the cooling pipe 81, and the gas component is supplied to the external device as medium pressure steam (for example, 1.0 to 2.5 MPaG).
- medium pressure steam for example, 1.0 to 2.5 MPaG
- a part of the slurry containing hydrocarbons and catalyst particles in the reactor main body 80 constituting the FT synthesis reactor 30 is extracted from the central portion of the reactor main body 80 and continuously introduced into the catalyst separator 36. Is done.
- the introduced slurry is filtered by a filter to capture the catalyst particles.
- the slurry is continuously separated into solid content and heavy hydrocarbon oil (hydrocarbon having approximately 11 or more carbon atoms), and the separated heavy hydrocarbon oil is continuously supplied to the second buffer tank 92. It is transferred to.
- the filter of the catalyst separator 36 is appropriately backwashed to remove the trapped particles from the filter surface and return to the reactor body 80. At this time, the catalyst particles captured by the filter are returned to the reactor main body 80 together with some liquid hydrocarbons.
- the reactor main body 80 has a gas phase portion above the slurry accommodated therein. Lightness that is a gas under the conditions in the reactor main body 80, which is generated by the reaction and moves to the gas phase part, with the unreacted synthesis gas that has moved up in the slurry and moved to the gas phase part beyond the slurry liquid level A mixture with hydrocarbons is continuously withdrawn from the top of the reactor body 80.
- the reactor main body 80 simultaneously with the synthesis step by the FT synthesis reaction, the heavy hydrocarbon oil that is a liquid phase extracted as a slurry from the central portion of the reactor main body 80, and the top of the reactor main body 80 A gas-liquid separation step of performing gas-liquid separation into a gas phase containing unreacted synthesis gas and light hydrocarbons extracted is performed.
- the catalyst constituting the slurry in the reactor main body 80 is not particularly limited, but a catalyst containing an inorganic oxide carrier such as silica and an active metal such as cobalt supported on the carrier is preferably used.
- the reaction conditions for the FT synthesis reaction in the reactor main body 80 are not limited.
- the following reaction conditions are preferably selected. That is, the reaction temperature is preferably 150 to 300 ° C. from the viewpoint of increasing the carbon monoxide conversion rate and the number of carbon atoms of the hydrocarbon to be produced. From the same viewpoint, the reaction pressure is preferably 0.5 to 5.0 MPa.
- the ratio (molar ratio) of hydrogen gas / carbon monoxide gas in the raw material gas is preferably 0.5 to 4.0. From the viewpoint of hydrocarbon production efficiency, the carbon monoxide conversion rate is desirably 50% or more.
- a mixture containing light hydrocarbons extracted from the top of the reactor main body 80 and unreacted synthesis gas is cooled in a gas-liquid separator 38 and condensed to light hydrocarbon oil (mainly carbon having 5 to 20 carbon atoms). Hydrogen) is continuously supplied to the first buffer tank 91.
- a gas component separated by the gas-liquid separator 38 that is, a mixture mainly composed of unreacted synthesis gas (carbon monoxide gas and hydrogen gas) and hydrocarbon gas having a small number of carbon atoms (four or less carbon atoms)
- the gas is recycled to the FT synthesis reactor 30, and the unreacted synthesis gas contained in the mixed gas is again used for the FT synthesis reaction.
- a part of the mixed gas is an FT synthesis reactor. Without being recycled to 30, it is introduced into a combustion facility (flare stack, not shown) outside the main body, burned, and then released into the atmosphere.
- the light hydrocarbon oil is extracted from the first buffer tank 91 and the heavy hydrocarbon oil is extracted from the second buffer tank 92.
- the light hydrocarbon oil extracted from the first buffer tank 91 and the heavy hydrocarbon oil extracted from the second buffer tank 92 are mixed in the pipe 96 and continuously supplied to the first fractionator 40. Supplied.
- the respective flow rates of the light hydrocarbon oil from the first buffer tank 91 and the heavy hydrocarbon oil from the second buffer tank 92 are calculated based on the set values of the reaction temperatures of the FT synthesis reaction in the synthesis step. And controlled to be equal to the respective estimated production rates of the light hydrocarbon oil and the heavy hydrocarbon oil in the synthesis process.
- the calculation of the estimated production rate of light hydrocarbon oil and heavy hydrocarbon oil in the synthesis step will be described in detail later.
- the extraction flow rate from each buffer tank By controlling the extraction flow rate from each buffer tank to be constant, due to temporary fluctuations such as the deviation of the reaction temperature from the set temperature or the fluctuation of the slurry liquid level in the synthesis process, Even if the liquid surface height fluctuates temporarily, the flow rates of the light hydrocarbon oil and the heavy hydrocarbon oil supplied to the first rectifying column 40 are constant, and are supplied to the first rectifying column 40. The composition and flow rate of the mixed oil of light hydrocarbon oil and heavy hydrocarbon oil are stabilized.
- the production speeds of the light hydrocarbon oil and the heavy hydrocarbon oil in the synthesis process, the light hydrocarbon oil extracted from the first buffer tank 91 and the heavy hydrocarbon oil extracted from the second buffer tank 92 By controlling each extraction flow rate equally, the liquid level of each buffer tank is caused by temporary fluctuations such as deviation of the reaction temperature from the set temperature in the synthesis process or fluctuation of the slurry liquid level. Even if the temperature fluctuates temporarily, inflow and extraction in each buffer tank are balanced in the long term, and the liquid level of each buffer tank is stabilized.
- the extraction flow rates of the light hydrocarbon oil from the first buffer tank and the heavy hydrocarbon oil from the second buffer tank are equal to the estimated production rates of the light hydrocarbon oil and heavy hydrocarbon oil in the synthesis process, respectively.
- the opening amounts of the first flow rate adjustment valve 95 and the second flow rate adjustment valve 97 are adjusted, and the light hydrocarbon oil from the first buffer tank 91 and the heavy hydrocarbon oil from the second buffer tank 92 are reduced. Each withdrawal flow rate is controlled.
- the reaction temperature set value of the FT synthesis reaction is input to the control unit 98, and the control unit 98 receives the first flow rate adjustment valve 95 and the second flow rate based on the input reaction temperature set value.
- the control valve 97 calculates a required valve opening, and outputs an instruction signal for setting the valve opening to the first flow control valve 95 and the second flow control valve 97.
- the liquid level height of the first buffer tank 91 and / or the second buffer tank 92 exceeds the upper limit value of the predetermined range, or falls below the lower limit value, the liquid level height.
- the first flow rate adjustment valve 95 and / or the second flow rate adjustment valve 97 is adjusted so that the value falls within a predetermined range. Or the response
- the chain growth probability varies mainly depending on the catalyst used and the reaction temperature.
- the chain growth probability indicates the probability of methylene chain growth, as described in, for example, Yasuhiro Onishi et al., “Transition and Future of GTL Technology Development”, Nippon Steel Engineering Technical Report, Vol.01 (2010). This is a parameter, and the larger this value, the greater the carbon number of the hydrocarbons produced. Moreover, the carbon number distribution of the produced
- the carbon number distribution of the generated hydrocarbon is assumed to follow the Anderson-Schulz-Flory distribution represented by the following formula.
- W n (1- ⁇ ) 2 n ⁇ n-1
- n represents the number of carbon atoms of the hydrocarbon produced by the FT synthesis reaction
- W n represents the mass fraction of the hydrocarbon product having n carbon atoms
- ⁇ represents the chain growth probability. From the above formula, as described in the above document, it is also possible to create a figure for estimating the carbon number distribution of the generated hydrocarbon with respect to each chain growth probability.
- the FT synthesis reaction is performed at a predetermined reaction temperature using a predetermined catalyst, if the chain growth probability at the catalyst and the reaction temperature can be known, the carbon number distribution of the generated hydrocarbon is estimated. .
- the chain growth probability for the same catalyst tends to be smaller as the reaction temperature is higher, and the chain growth probability at each reaction temperature of a given catalyst is the FT synthesis reaction operation using the catalyst and changing the temperature.
- the range of the number of carbon atoms of hydrocarbons (light hydrocarbons) that are extracted from the top of the reactor body 80 and become gases under the reaction conditions in the reactor body 80 is the hydrocarbons produced by the FT synthesis reaction.
- the carbon number range of the hydrocarbons contained in the light hydrocarbon oil obtained under each reaction condition can be grasped. If the carbon number distribution of the hydrocarbon produced by the FT synthesis reaction at a specific reaction temperature and the range of the carbon number of the hydrocarbon contained in the light hydrocarbon oil obtained at that time are estimated, these information and reaction steps
- the production rate of light hydrocarbon oil can be estimated from the data of carbon monoxide conversion and hydrocarbon selectivity in. If the production rate of the light hydrocarbon oil is estimated, the production rate of the remaining heavy hydrocarbon oil is also estimated.
- the first buffer is based on the estimated production rate values of the light hydrocarbon oil and the heavy hydrocarbon oil determined almost uniquely with respect to the set reaction temperature of the FT synthesis reaction.
- the first flow rate control valve 95 and the second flow rate control valve 97 are respectively adjusted so that the flow rates withdrawn from the tank 91 and the second buffer tank 92 are equal to the production rates of the light hydrocarbon oil and the heavy hydrocarbon oil, respectively. To control.
- the production rate of light hydrocarbon oil and heavy hydrocarbon oil in the synthesis process is estimated based on the relationship between the reaction temperature of the FT synthesis reaction and the chain growth probability as described above. You may perform based on the driving
- the mixed oil is fractionated to obtain a naphtha fraction (a fraction having a boiling point lower than about 150 ° C), an intermediate fraction (a boiling point of about 150 to about 360 ° C), a wax It is fractionated into fractions (fractions with boiling points above about 360 ° C.).
- a wax fraction (mainly having 21 or more carbon atoms) extracted from the bottom of the first rectifying column 40 is supplied to the wax fraction hydrocracking reactor 50 and extracted from the center of the first rectifying column 40.
- the middle distillate discharged (mainly having 11 to 20 carbon atoms) is supplied to the middle distillate hydrotreating reactor 52, and liquid hydrocarbons (mainly, naphtha distillate extracted from the top of the first rectifying tower 40 are mainly used.
- the carbon number of 5 to 10) is supplied to the naphtha fraction hydrotreating reactor.
- hydrotreating means hydrocracking of a wax fraction, hydrorefining of a middle fraction, and hydrorefining of a naphtha fraction.
- the wax fraction supplied from the bottom of the first fractionator 40 is hydrocracked using the hydrogen gas supplied from the hydrogen separator 26. The carbon number is reduced to approximately 20 or less.
- a product hydrocracked in the wax fraction hydrocracking reactor 50 (including undecomposed wax) is separated into a gas component and a liquid component in a gas-liquid separator 56, of which liquid is a liquid hydrocarbon.
- the fraction is transferred to the second fractionator 70, and the gaseous fraction containing hydrogen gas and gaseous hydrocarbons is supplied to the middle fraction hydrotreating reactor 52 and the naphtha fraction hydrotreating reactor 54. Hydrogen gas is reused.
- the middle distillate liquid hydrocarbon supplied from the center of the first rectifying column 40 is fed from the hydrogen separator 26 to the wax distillate hydrogen.
- Hydrogen purification is performed using hydrogen gas supplied through the hydrocracking reactor 50.
- the liquid hydrocarbon is hydroisomerized to obtain isoparaffin mainly for the purpose of improving the low temperature fluidity as a fuel oil base material.
- Hydrogen is added to the unsaturated hydrocarbon contained to convert it to saturated hydrocarbon.
- oxygen-containing compounds such as alcohols contained in the hydrocarbon are hydrodeoxygenated and converted into saturated hydrocarbons and water.
- the product containing liquid hydrocarbons hydrotreated in this way is separated into a gas and a liquid by the gas-liquid separator 58, and the liquid component which is liquid hydrocarbons in the second fractionator 70.
- the gas component that is transferred and contains hydrogen gas and gaseous hydrocarbons is subjected to the above-described hydrotreating reaction, and the hydrogen gas is reused.
- the liquid hydrocarbon of the naphtha fraction supplied from the upper part of the first rectifying column 40 is passed from the hydrogen separator 26 through the wax fraction hydrocracking reactor 50. Hydrogen purification is performed using the supplied hydrogen gas. Thereby, oxygen-containing compounds such as unsaturated hydrocarbons and alcohols contained in the supplied naphtha fraction are converted into saturated hydrocarbons.
- the liquid hydrocarbon-purified product containing the liquid hydrocarbon is separated into a gas component and a liquid component by the gas-liquid separator 60, and the liquid component, which is a liquid hydrocarbon, is transferred to the naphtha stabilizer 72.
- the gas component containing hydrogen gas and gaseous hydrocarbon is reused for the hydrotreating reaction.
- the liquid hydrocarbons supplied from the wax fraction hydrocracking reactor 50 and the middle fraction hydrotreating reactor 52 as described above are hydrocarbons having 10 or less carbon atoms.
- Boiling point is lower than about 150 ° C.
- kerosene fraction (boiling point is about 150 to 250 ° C.)
- light oil fraction (boiling point is about 250 to 360 ° C.)
- wax fraction hydrocracking reactor 50 It is fractionated into an undecomposed wax fraction that has not been sufficiently decomposed (boiling point above about 360 ° C.).
- an undecomposed wax fraction is extracted from the bottom of the second fractionator 70, a light oil fraction is extracted from the lower part, a kerosene fraction is extracted from the center, and from the top of the tower, Hydrocarbons having 10 or less carbon atoms are extracted and supplied to the naphtha stabilizer 72.
- hydrocarbons having 10 or less carbon atoms supplied from the naphtha fraction hydrotreating reactor 54 and the second rectifying column 70 are distilled to obtain naphtha as a product (5 to 5 carbon atoms). 10) is obtained. Thereby, high-purity naphtha is taken out from the bottom of the naphtha stabilizer 72.
- flare gas mainly composed of hydrocarbons having 4 or less carbon atoms, which is not a product target is discharged. This flare gas is introduced into an external combustion facility (not shown), burned, and then released into the atmosphere.
- the first flow rate adjustment valve 95 and the second flow rate adjustment valve 97 are adjusted based on the liquid level height of the first buffer tank 91 and the second buffer tank 92. Rather, the production rates of the light hydrocarbon oil and the heavy hydrocarbon oil estimated based on the set reaction temperature of the FT synthesis reaction, the light hydrocarbon oil from the first buffer tank 91 and the second buffer tank. The first flow rate adjustment valve 95 and the second flow rate adjustment valve 97 are adjusted so that the flow rates of the heavy hydrocarbon oil extracted from each of the fuel oils become equal.
- the hydrocarbon production method of the present invention has been described along the preferred embodiment.
- the present invention is not limited to the above-described embodiment, and can be changed without departing from the gist of the present invention. it can.
- the FT synthesis reaction is performed in a bubble column type slurry bed reactor, but a fixed bed reactor may be used.
- the gas-liquid separation step of the reaction product is performed in a gas-liquid separation device provided in the subsequent stage of the reactor.
- the control unit 98 is provided to adjust the first flow rate adjustment valve 95 and the second flow rate adjustment valve 97 to control the flow rates of light hydrocarbon oil and heavy hydrocarbon oil.
- the control unit 98 is not provided, and an operator obtains an estimated value of the production rate of light hydrocarbon oil and heavy hydrocarbon oil based on the set reaction temperature of the synthesis process, and manually based on the estimated value.
- the flow rates of the first flow rate adjustment valve 95 and the second flow rate adjustment valve 97 may be adjusted.
- the fractionation step the fraction is divided into three fractions, that is, a wax fraction, a middle fraction, and a naphtha fraction, but light carbonization other than the wax fraction and the wax fraction is performed. You may fractionate into two fractions of a hydrogen fraction. In that case, in the upgrading step, purification is performed by hydrocracking the wax fraction and hydrotreating the light hydrocarbon fraction.
- the second fractionator 70 is fractionated into four fractions of hydrocarbons having 10 or less carbon atoms, a kerosene fraction, a light oil fraction, and an undecomposed wax.
- the distillate and light oil fraction may be combined and fractionated into three fractions as intermediate fractions.
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Abstract
Description
本願は、2010年3月30日に出願された特願2010-79551号について優先権を主張し、その内容をここに援用する。
FT合成反応により炭化水素を合成する合成反応システムとしては、例えば、反応器内にて、液体炭化水素に触媒粒子を懸濁させたスラリーに合成ガスを吹き込んでFT合成反応を行なう気泡塔型スラリー床FT合成反応システムが開示されている(特許文献1)。
精留塔においては、軽質炭化水素油及び重質炭化水素油の混合油が、例えば、精留塔の塔頂から抜き出されるナフサ留分、精留塔の中央部から抜き出される中間留分、精留塔の塔底から抜き出されるワックス留分に分留される。得られた各留分は、それぞれ水素化処理及び分留を行う工程であるアップグレーディング工程を経て、各種燃料基材となる。
従来のFT合成反応システムにおいては、各バッファタンクへの軽質炭化水素油及び重質炭化水素油の流入量が変動しても各バッファタンクの液面高さが一定になるように、各バッファタンクからの軽質炭化水素油及び重質炭化水素油のそれぞれの抜き出し流量が調整されていた。ところが、このように抜き出し流量が調整されると、精留塔に供給される軽質炭化水素油と重質炭化水素油との比率、及び合計の流量が変動しやすかった。
後段のアップグレーディング工程に良質な各原料留分を供給するためには、精留塔における各留分の蒸留カットを一定に保つ、すなわち、精留塔の各留分の抜き出し段トレイ温度を一定に保つ必要がある。しかし、精留塔入口における軽質炭化水素油と重質炭化水素油との比率が変動する場合、精留塔からの各留分の抜き出し量を変更することで抜き出し段トレイ温度を一定に保つことになるが、上記変動に追随しきれないことがある。そのため、抜き出した各留分の組成を一定に保つことが困難であった。
本発明は、前記事情に鑑みてなされたものであり、FT合成反応における一時的な反応温度の設定値からの乖離又はスラリー液面高さの変動が生じた際の、精留塔に供給する軽質炭化水素油と重質炭化水素油との比率及び流量の変動を抑制できる炭化水素の製造方法を提供することを目的とする。
すなわち、本発明の炭化水素の製造方法は、触媒の存在下、連続的に供給される水素ガスと一酸化炭素ガスとからフィッシャー・トロプシュ合成反応により炭化水素を合成する合成工程と、気液分離により、前記炭化水素を軽質炭化水素と重質炭化水素油とに分離する気液分離工程と、前記軽質炭化水素から得られる軽質炭化水素油及び前記重質炭化水素油をそれぞれ、各バッファタンクに連続的に供給する一時貯留工程と、前記各バッファタンクから前記軽質炭化水素油及び重質炭化水素油をそれぞれ連続的に抜き出し、軽質炭化水素油と重質炭化水素油とを混合して精留塔に供給する抜き出し工程と、前記軽質炭化水素油と重質炭化水素油との混合油を、少なくともワックス留分とワックス留分よりも軽質な留分とに分留する分留工程と、を備える。
本発明の炭化水素の製造方法においては、前記合成工程における設定反応温度に基づいて、軽質炭化水素油及び重質炭化水素油のそれぞれの推定生成速度を求め、前記抜き出し工程における軽質炭化水素油及び重質炭化水素油の抜き出し流量を、前記それぞれの推定生成速度と等しくなるように制御する。
まず、本発明の炭化水素の製造方法が使用される液体燃料製造システムの一例について説明する。
図1に、液体燃料製造システムの一例を示す。
この液体燃料製造システム1は、合成ガス製造ユニット3と、FT合成ユニット5と、アップグレーディングユニット7とを備えている。合成ガス製造ユニット3においては、炭化水素原料である天然ガスを改質して一酸化炭素ガスと水素ガスを含む合成ガスが製造される。FT合成ユニット5においては、合成ガス製造ユニット3において製造された合成ガスからFT合成反応により炭化水素が合成される。本例においては、FT合成反応器として気泡塔型スラリー床FT合成反応器を用いる例を示す。アップグレーディングユニット7においては、FT合成ユニット5において合成された炭化水素が水素化処理及び分留されて液体燃料(ナフサ、灯油、軽油)の基材、及びワックス等が製造される。
脱硫装置10は、水素化脱硫反応器等を含み、原料である天然ガスから硫黄化合物を除去する。
改質器12においては、脱硫装置10から供給された天然ガスが例えば水蒸気・炭酸ガス改質法により改質されて、一酸化炭素ガス(CO)と水素ガス(H2)とを主成分として含む合成ガスが製造される。
排熱ボイラー14においては、改質器12にて製造された合成ガスの排熱が回収されて高圧スチームが得られる。
気液分離器16においては、排熱ボイラー14にて高温の合成ガスとの熱交換により加熱された水が気体(高圧スチーム)と液体の水とに分離される。
気液分離器18においては、排熱ボイラー14にて冷却された合成ガスから凝縮分が除去され、気体分が脱炭酸装置20に供給される。
脱炭酸装置20は、気液分離器18から供給された合成ガスから吸収液を用いて炭酸ガスを吸収・除去する吸収塔22と、当該炭酸ガスを含む吸収液から炭酸ガスを除去して再生する再生塔24とを有する。
水素分離装置26においては、脱炭酸装置20により炭酸ガスが分離された合成ガスから、当該合成ガスに含まれる水素ガスの一部が分離される。
FT合成反応器30は、FT合成反応により合成ガスから液体炭化水素を合成する反応器であり、反応器本体80と、冷却管81とを主に備えている。
反応器本体80は、略円筒型の金属製の容器であって、その内部には、液体炭化水素(FT合成反応の生成物)中に固体の触媒粒子を懸濁させたスラリーが収容されている。
この反応器本体80の下部においては、一酸化炭素ガス及び水素ガスを主成分とする合成ガスがスラリー中に噴射されるようになっている。そして、スラリー中に吹き込まれた合成ガスは、気泡となってスラリー中を反応器本体80の高さ方向(鉛直方向)下方から上方へ向かって上昇するようになっている。その過程にて、合成ガスは液体炭化水素中に溶解し、触媒粒子と接触することにより、炭化水素の合成(FT合成反応)が進行する。
また、合成ガスが気泡として反応器本体80内を上昇することにより、反応器本体80の内部においてはスラリーの上昇流(エアリフト)が生じる。これにより、反応器本体80内部に、スラリーの循環流が生じる。なお、反応器本体80内の塔頂まで上昇した未反応の合成ガス及びFT合成反応により生成した、反応器本体80内の条件において気体である炭化水素は、反応器本体80の塔頂から抜き出される。本願においては、前記反応器本体80内の条件において気体である炭化水素を「軽質炭化水素」という。
気液分離器34においては、FT合成反応器30内に配設された冷却管81内を流通して加熱された水が、水蒸気(中圧スチーム)と液体の水とに分離される。
FT合成反応器30の頂部より抜き出された未反応合成ガス及び軽質炭化水素は、気液分離器38に導入され、冷却される。更に、冷却により凝縮した液体成分と未反応の合成ガス及び主として炭素数4以下の炭化水素ガスからなる気体成分とが分離される。本願においては、この液体成分を、「軽質炭化水素油」という。ここで、軽質炭化水素油は、主としてナフサ留分及び中間留分相当の炭化水素からなる。
触媒分離器36においては、FT合成反応器30の中央部より抜き出されたスラリーが触媒と液体炭化水素生成物とに分離される。本願においては、気液分離器36にて得られた液体炭化水素生成物を「重質炭化水素油」という。ここで、重質炭化水素油は、軽質炭化水素より重質の炭化水素からなる。
第1精留塔40においては、FT合成反応器30から触媒分離器36を介して供給された重質炭化水素油と、気液分離器38を介して供給された軽質炭化水素油とが混合された混合油が分留され、沸点に応じて各留分(ナフサ留分、中間留分、ワックス留分)に分離される。ここで、ナフサ留分は沸点が約150℃より低い留分、中間留分は沸点が約150~360℃の留分、ワックス留分は沸点が約360℃を超える留分である。
また、第2バッファタンク92と加熱器93とを接続する配管96には第2流量調節弁97が取り付けられ、第1バッファタンク91と配管96とを接続する配管94には第1流量調節弁95が取り付けられている。
さらに、FT合成ユニット5は、FT合成反応の反応温度設定値が入力され、その温度情報に基づいて第1流量調節弁95及び第2流量調節弁97の弁開度を調節する制御部98を備えている。
第1バッファタンク91及び第2バッファタンク92には、液面高さを測定するレベル計91a、92aが設置されている。レベル計91a、92aとしては、例えば、マグネット式のレベル計などが用いられる。
ワックス留分水素化分解反応器50は、第1精留塔40の塔底に接続されて、ワックス留分が供給されるようになっている。
中間留分水素化精製反応器52は、第1精留塔40の中央部に接続されて、中間留分が供給されるようになっている。
ナフサ留分水素化精製反応器54は、第1精留塔40の塔頂に接続されて、ナフサ留分が供給されるようになっている。
気液分離器56、58、及び60は、これら反応器50、52、及び54のそれぞれに対応して設けられている。
第2精留塔70においては、気液分離器56及び58から供給された液体炭化水素が沸点に応じて分留される。
ナフサ・スタビライザー72は、気液分離器60及び第2精留塔70から供給されたナフサ留分に含まれる液体炭化水素が分留されて、炭素数4以下の気体成分はフレアガスとして排出され、炭素数が5以上の成分は製品のナフサとして回収される。
上記液体燃料製造システム1を構成するFT合成ユニットを主として利用する、本発明の炭化水素の製造方法の一実施形態例について説明する。
本実施形態例においては、メタンを主成分とする天然ガスが合成ガス製造ユニット3に供給され、改質されて合成ガス(一酸化炭素ガスと水素ガスを主成分とする混合ガス)が製造される。
具体的には、上記合成ガス製造ユニット3において製造された合成ガスは、FT合成反応器30を構成する反応器本体80の底部から流入して、反応器本体80内に貯留されたスラリー内を上昇する。この際、反応器本体80内においては、上述したFT合成反応により、当該合成ガスに含まれる一酸化炭素ガスと水素ガスとが反応して、炭化水素が生成する。
さらに、この合成反応の際には、冷却管81内に水が流通されて、FT合成反応の反応熱が除去され、この熱交換により加熱された水が気化して水蒸気となる。この水蒸気は、気液分離器34にて液化した水が冷却管81に戻されて、気体分が中圧スチーム(例えば1.0~2.5MPaG)として外部装置に供給される。
触媒分離器36のフィルターは、捕捉した粒子をフィルター表面から取り除くと共に反応器本体80に戻すために適宜逆洗される。このとき、フィルターにより捕捉された触媒粒子は、一部の液体炭化水素と共に反応器本体80に戻される。
すなわち、反応器本体80においては、FT合成反応による合成工程と同時に、反応器本体80の中央部からスラリーとして抜き出される液相である重質炭化水素油と、反応器本体80の塔頂から抜き出される未反応の合成ガス及び軽質炭化水素を含む気相とに気液分離する気液分離工程が行われることとなる。
また、反応器本体80内におけるFT合成反応の反応条件としては限定されないが、例えば次のような反応条件が好ましく選択される。すなわち、反応温度は、一酸化炭素転化率及び生成する炭化水素の炭素数を高めるとの観点から、150~300℃であることが好ましい。同様の観点から、反応圧力は0.5~5.0MPaであることが好ましい。原料ガス中の水素ガス/一酸化炭素ガスの比率(モル比)は0.5~4.0であることが好ましい。なお、炭化水素の生産効率の観点から、一酸化炭素転化率は50%以上であることが望ましい。
反応器本体80の頂部から抜き出された軽質炭化水素と未反応の合成ガスを含む混合物は、気液分離器38において冷却されて、凝縮した軽質炭化水素油(主として炭素数5~20の炭化水素)が第1バッファタンク91に連続的に供給される。一方、気液分離器38にて分離されたガス分、すなわち未反応の合成ガス(一酸化炭素ガスと水素ガス)と炭素数が少ない(炭素数4以下)炭化水素ガスを主成分とする混合ガスは、FT合成反応器30にリサイクルされ、混合ガスに含まれる未反応の合成ガスは再度FT合成反応に供される。なお、前記混合ガスのリサイクルにより、主として炭素数4以下の気体状炭化水素がFT合成反応系内に高濃度に蓄積することを防止する目的で、前記混合ガスの一部は、FT合成反応器30にリサイクルされずに、本体外部の燃焼設備(フレアースタック、図示せず)に導入されて、燃焼された後に大気放出される。
次いで、第1バッファタンク91から軽質炭化水素油が抜き出されると共に、第2バッファタンク92から重質炭化水素油が抜き出される。第1バッファタンク91から抜き出された軽質炭化水素油と第2バッファタンク92から抜き出された重質炭化水素油とは配管96内にて混合され、第1精留塔40に連続的に供給される。
その際、第1バッファタンク91からの軽質炭化水素油及び第2バッファタンク92からの重質炭化水素油のそれぞれの抜き出し流量が、合成工程におけるFT合成反応の反応温度の設定値に基づいて算出される、合成工程における軽質炭化水素油及び重質炭化水素油のそれぞれの推定生成速度と等しくなるように制御される。なお、合成工程における軽質炭化水素油及び重質炭化水素油の推定生成速度の算出については、後に詳述する。
また、合成工程における軽質炭化水素油及び重質炭化水素油の各生成速度と、第1バッファタンク91から抜き出される軽質炭化水素油及び第2バッファタンク92から抜き出される重質炭化水素油の各抜き出し流量のそれぞれが等しく制御されることにより、合成工程における反応温度の設定温度からの乖離、あるいはスラリー液面高さの変動といった一時的な変動に起因して、各バッファタンクの液面高さが一時的に変動しても、長期的には、各バッファタンクにおける流入と抜き出しが均衡し、各バッファタンクの液面高さも安定化する方向となる。
FT合成反応においては、主として、使用する触媒及び反応温度によって、連鎖成長確率が変化する。ここで連鎖成長確率は、例えば、大西康博他、「GTL技術の開発の変遷と将来」、新日鉄エンジニアリング技報、Vol.01 (2010)に記載されるように、メチレン鎖の成長する確率を示すパラメータであり、この値が大きいほど、生成する炭化水素の炭素数が増加する。また、この値により、生成する炭化水素の炭素数分布が推定される。すなわち、生成する炭化水素の炭素数分布は、下記式で表されるAnderson-Schulz-Flory分布に従うとされている。
Wn=(1-α)2nαn-1
ここで、nはFT合成反応により生成する炭化水素の炭素数、Wnは炭素数nの炭化水素生成物の質量分率、αは連鎖成長確率を表す。
上記式により、前記文献にも記載されるように、各連鎖成長確率に対する生成炭化水素の炭素数分布を推定する図を作成することもできる。
したがって、所定の触媒を使用し、所定の反応温度によってFT合成反応を行なう場合に、当該触媒、当該反応温度における連鎖成長確率を知ることができれば、生成する炭化水素の炭素数分布が推定される。
そして、同一の触媒についての連鎖成長確率は、反応温度が高いほど小さくなる傾向にあり、所定の触媒の各反応温度における連鎖成長確率は、当該触媒を使用し、温度を変えたFT合成反応運転における生成物の分析から予め把握することができる(図2の例を参照)。
一方、反応器本体80の塔頂から抜き出される、反応器本体80内の各反応条件において気体となる炭化水素(軽質炭化水素)の炭素数の範囲は、FT合成反応により生成する各炭化水素の物性データよりの推定、あるいは過去の運転における分析結果等の手段により把握することができる。よって、各反応条件において得られる軽質炭化水素油に含まれる炭化水素の炭素数の範囲を把握することができる。
特定の反応温度におけるFT合成反応により生成する炭化水素の炭素数分布、及びその際に得られる軽質炭化水素油に含まれる炭化水素の炭素数の範囲が推定されれば、これらの情報及び反応工程における一酸化炭素転化率及び炭化水素選択率のデータから、軽質炭化水素油の生成速度が推定される。軽質炭化水素油の生成速度が推定されれば、その残余分である重質炭化水素油の生成速度も推定される。
上記制御部98においては、上記により、FT合成反応の設定反応温度に対してほぼ一義的に決定される軽質炭化水素油及び重質炭化水素油の推定生成速度の値を基に、第1バッファタンク91及び第2バッファタンク92からの抜き出し流量が、それぞれ前記軽質炭化水素油及び重質炭化水素油の各生成速度と等しくなるように、それぞれ第1流量調節弁95及び第2流量調節弁97を制御する。
第1精留塔40においては、前記混合油が分留されて、ナフサ留分(沸点が約150℃より低い留分)と、中間留分(沸点が約150~約360℃)と、ワックス留分(沸点が約360℃を超える留分)とに分別される。この第1精留塔40の塔底から抜き出されるワックス留分(主として炭素数21以上)は、ワックス留分水素化分解反応器50に供給され、第1精留塔40の中央部から抜き出される中間留分(主として炭素数11~20)は、中間留分水素化精製反応器52に供給され、第1精留塔40の塔頂から抜き出されるナフサ留分の液体炭化水素(主として炭素数5~10)は、ナフサ留分水素化精製反応器54に供給される。
以下、上記本実施形態により製造された炭化水素から、水素化処理及び分留により液体燃料基材を製造するアップグレーディング工程の例について説明する。
なお、ここで、「水素化処理」とは、ワックス留分の水素化分解、中間留分の水素化精製、及びナフサ留分の水素化精製を意味する。
ワックス留分水素化分解反応器50においては、第1精留塔40の塔底から供給されたワックス留分が、上記水素分離装置26から供給される水素ガスを利用して水素化分解されて、その炭素数が概ね20以下に低減される。この水素化分解反応においては、炭素数の多い炭化水素の炭素-炭素結合を切断して、炭素数の少ない低分子量の炭化水素を生成する。同時に、ワックス留分を主として構成するノルマルパラフィンの一部は、水素化異性化されてイソパラフィンに転換される。また、ワックス留分に含まれる不飽和炭化水素は水素化され、飽和炭化水素となる。更に、ワックス留分に含まれる、アルコール類等の含酸素化合物は、水素化脱酸素により、飽和炭化水素と水とに転換される。なお、ワックス留分の一部は、所望の程度まで水素化分解されず、未分解ワックスとして水素化分解生成物と共にワックス留分水素化分解反応器50から排出される。ワックス留分水素化分解反応器50にて水素化分解された生成物(未分解ワックスを含む)は、気液分離器56において気体分と液体分とに分離され、そのうち液体炭化水素である液体分は、第2精留塔70に移送され、水素ガス及び気体状の炭化水素を含む気体分は、中間留分水素化精製反応器52及びナフサ留分水素化精製反応器54に供給されて、水素ガスが再利用される。
例えば、上記実施形態においては、FT合成反応を気泡塔型スラリー床反応器において実施しているが、固定床反応器を用いてもよい。その場合、反応生成物の気液分離工程は、反応器の後段に設けられる気液分離装置において実施される。
また、上記実施形態においては、第1流量調節弁95及び第2流量調節弁97を調整して、軽質炭化水素油及び重質炭化水素油の抜き出し流量を制御するために、制御部98を備えたが、制御部98を備えず、作業者が合成工程の設定反応温度に基づき、軽質炭化水素油及び重質炭化水素油の生成速度の推定値を求め、該推定値に基づいて、手動により第1流量調節弁95及び第2流量調節弁97の流量を調節してもよい。
また、上記実施形態においては、分留工程において、ワックス留分、中間留分、及びナフサ留分の3つの留分に分留しているが、ワックス留分とワックス留分以外の軽質の炭化水素留分の2つの留分に分留してもよい。その場合、アップグレーディング工程において、ワックス留分の水素化分解と前記軽質の炭化水素留分の水素化精製により精製を行うこととなる。
また、上記実施形態においては、第2精留塔70において、炭素数10以下の炭化水素、灯油留分、軽油留分、及び未分解ワックスの4つの留分に分留しているが、灯油留分と軽油留分を併せて中間留分として3つの留分に分留してもよい。
40 第1精留塔
80 反応器本体
91 第1バッファタンク
92 第2バッファタンク
95 第1流量調節弁
97 第2流量調節弁
98 制御部
Claims (3)
- 触媒の存在下、連続的に供給される水素ガスと一酸化炭素ガスとからフィッシャー・トロプシュ合成反応により炭化水素を合成する合成工程と、
気液分離により、前記炭化水素を軽質炭化水素と重質炭化水素油とに分離する気液分離工程と、
前記軽質炭化水素から得られる軽質炭化水素油及び前記重質炭化水素油をそれぞれ、各バッファタンクに連続的に供給する一時貯留工程と、
前記各バッファタンクから前記軽質炭化水素油及び重質炭化水素油をそれぞれ連続的に抜き出し、軽質炭化水素油と重質炭化水素油とを混合して精留塔に供給する抜き出し工程と、
前記軽質炭化水素油と重質炭化水素油との混合油を、少なくともワックス留分とワックス留分よりも軽質な留分とに分留する分留工程と、
を備える炭化水素の製造方法であって、
前記合成工程における設定反応温度に基づいて、軽質炭化水素油及び重質炭化水素油のそれぞれの推定生成速度を求め、前記抜き出し工程における軽質炭化水素油及び重質炭化水素油それぞれの抜き出し流量を、前記それぞれの推定生成速度と等しくなるように制御する炭化水素の製造方法。 - 前記合成工程及び気液分離工程が、上部に気相部を有するスラリー床型反応器内で行われる請求項1記載の炭化水素の製造方法。
- 前記軽質炭化水素油及び重質炭化水素油の推定生成速度が、前記合成工程において使用する触媒に関する、フィッシャー・トロプシュ合成反応の反応温度と連鎖成長確率の関係に基づいてそれぞれ求められる請求項1又は2記載の炭化水素の製造方法。
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