CN111944553A - Method for cascade Fischer-Tropsch synthesis reaction - Google Patents
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- 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
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- 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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- C10G2/342—Apparatus, reactors with moving solid catalysts
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- C10G2/00—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon
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Abstract
The invention discloses a method for cascade Fischer-Tropsch synthesis reaction. It comprises the following steps: containing CO and H2The synthesis gas is catalyzed by a catalyst to carry out Fischer-Tropsch synthesis reaction when sequentially passing through a plurality of stages of Fischer-Tropsch synthesis reactors connected in series, and hydrocarbon products and water generated by each stage of Fischer-Tropsch synthesis reactor are separated separately and then are merged and discharged out of the system; wherein the flow direction of the synthesis gas and the flow direction of the catalyst are cocurrent and/or countercurrent. On one hand, the invention effectively utilizes the catalyst, thereby not only reducing the consumption of the catalyst, but also improving the activity of the catalyst; on the other hand, the conversion rate of the synthetic gas can be improved, and the total oil production capacity is increased.
Description
Technical Field
The invention relates to a method for cascade Fischer-Tropsch synthesis reaction, belonging to the field of synthesis gas conversion.
Background
In the 20 th century, German Franz Fischer and Hans Tropsch discovered CO and H2The reaction (generally called as synthesis gas) can generate hydrocarbon under the action of a catalyst under the conditions of proper temperature, pressure and the like, so the reaction is called as Fischer-Tropsch synthesis reaction. Coal, natural gas, biomass, residual oil and the like are gasified or reformed to generate synthesis gas, hydrocarbons and oxygen-containing compounds with various carbon numbers can be generated through Fischer-Tropsch synthesis reaction, and further the hydrocarbons and the oxygen-containing compounds can be converted into clean liquid fuels and/or chemicals with high added values. Thus, the fischer-tropsch synthesis reaction is of great importance in carbon-one chemistry.
The Fischer-Tropsch synthesis reaction is a strong exothermic reaction, and the design of a reactor is the key for the success of the process. The slurry bed reactor has the advantages of uniform bed temperature distribution, convenient heat transfer, on-line replacement of the catalyst, easy amplification, high monomer capacity, stable operation and the like, and is an ideal Fischer-Tropsch synthesis reactor. The fluidized bed gas-solid reactor is also an ideal reactor form because the fluidized bed gas-solid reactor has the advantages of better heat transfer characteristic at high temperature, online replacement of a catalyst, large treatment capacity, favorability for generating low-carbon olefin and the like. However, for the two types of Fischer-Tropsch synthesis reactors, although the catalyst can be replaced on line and the bed temperature is uniform and easy to control, the following problems still exist:
1. for slurry bed reactors and fluidized bed reactors, the catalyst needs to be continuously replaced to maintain higher catalyst activity in the reactor and realize stable high conversion rate. In this case, a certain proportion of catalyst is discharged each time, resulting in a large waste of catalyst and an increase in the cost per ton of catalyst.
2. As can be seen from the formula (1), water is the main product of the Fischer-Tropsch synthesis reaction, but unfortunately, water can cause hydrothermal deactivation of most Fischer-Tropsch synthesis catalysts, and the catalysts are easy to break and have reduced stability. Thus, fischer-tropsch synthesis processes typically employ as low a per pass conversion as possible, avoiding water accumulation in the gas phase loop. This results in low overall conversion, reduced syngas utilization and increased gas-to-fuel consumption. How to increase the synthesis gas conversion rate is the key to the optimization of the process integration.
CO+H2＝-CH2-+H2O (1)
3. Sulfur is a poison of the Fischer-Tropsch synthesis catalyst and is a main reason for the deactivation of the Fischer-Tropsch synthesis catalyst. For the fischer-tropsch synthesis process using a slurry or fluidised bed reactor, the effect of sulphur poisoning is much greater than for the fixed bed reactor process, because once sulphur enters the slurry or fluidised bed reactor, the catalyst of the whole reaction system is at risk of deactivation, and the total replacement cost is very high, unlike the fixed bed reactor, where sulphur only gradually erodes downwards from the top of the reactor to cause deactivation. Therefore, the fischer-tropsch synthesis process using a slurry or fluidized bed reactor has very strict requirements for the sulfur content in the synthesis gas.
Disclosure of Invention
The invention aims to provide a method for cascade Fischer-Tropsch synthesis reaction, which effectively utilizes a catalyst, can reduce the consumption of the catalyst and can improve the activity of the catalyst; on the other hand, the conversion rate of the synthetic gas can be improved, and the total oil production capacity is increased.
The invention provides a method for cascade Fischer-Tropsch synthesis reaction, which comprises the following steps: containing CO and H2The synthesis gas is catalyzed by a catalyst to carry out Fischer-Tropsch synthesis reaction when sequentially passing through a plurality of stages of Fischer-Tropsch synthesis reactors connected in series, and hydrocarbon products and water generated by each stage of Fischer-Tropsch synthesis reactor are separated independently and then are merged and discharged out of the system;
wherein the flow direction of the synthesis gas and the flow direction of the catalyst are cocurrent and/or countercurrent;
1) when the flow direction of the synthesis gas and the flow direction of the catalyst are in parallel flow, along the flow direction of the synthesis gas, the catalyst enters from the first-stage Fischer-Tropsch synthesis reactor and replaces an equilibrium catalyst, and the equilibrium catalyst continuously catalyzes the Fischer-Tropsch synthesis reaction in the next-stage Fischer-Tropsch synthesis reactor until the catalyst is discharged from the last-stage Fischer-Tropsch synthesis reactor;
2) and when the flow direction of the synthesis gas and the flow direction of the catalyst are in counter-flow, the catalyst replaces an equilibrium catalyst after entering from the last stage of the Fischer-Tropsch synthesis reactor against the flow direction of the synthesis gas, and the equilibrium catalyst continuously catalyzes the Fischer-Tropsch synthesis reaction in the previous stage of the Fischer-Tropsch synthesis reactor until the catalyst is discharged from the first stage of the Fischer-Tropsch synthesis reactor.
In the above process, the fischer-tropsch synthesis reactors connected in series in multiple stages may preferably be fischer-tropsch synthesis reactors connected in series in 2 stages.
In the invention, when the reactor is a 2-stage Fischer-Tropsch synthesis reactor connected in series and the flow direction of the synthesis gas and the flow direction of the catalyst are in parallel flow, the first stage Fischer-Tropsch synthesis reactor along the synthesis gas inlet direction is a main reactor, and the later stage is an auxiliary reactor;
when the reactor is a 2-stage Fischer-Tropsch synthesis reactor connected in series and the flowing direction of the synthesis gas and the flowing direction of the catalyst are in counter flow, the Fischer-Tropsch synthesis reactor at the first stage along the entering direction of the synthesis gas is a pre-reaction system, and the Fischer-Tropsch synthesis reactor at the later stage is a main reaction system.
In the method, each stage of Fischer-Tropsch synthesis reactor is one or more slurry bed reactors and/or fluidized bed reactors connected in parallel; when the flow direction of the synthesis gas and the flow direction of the catalyst are in parallel flow, the number of the parallel-connected slurry bed reactors and/or fluidized bed reactors in the Fischer-Tropsch synthesis reactor at the next stage is less than or equal to that of the previous stage, and preferably the number of the parallel-connected slurry bed reactors and/or fluidized bed reactors in the Fischer-Tropsch synthesis reactor at the next stage is less than that of the previous stage; and when the flow direction of the synthesis gas and the flow direction of the catalyst are in a counter-current manner, the number of the parallel-connected slurry bed reactors and/or fluidized bed reactors in the Fischer-Tropsch synthesis reactor at the later stage is more than or equal to that of the previous stage, and preferably, the number of the parallel-connected slurry bed reactors and/or fluidized bed reactors in the Fischer-Tropsch synthesis reactor at the later stage is more than that of the previous stage.
In the above method, the fluidized bed reactor is specifically a circulating fluidized bed reactor and/or a fixed fluidized bed reactor.
In the above method, when the equilibrium catalyst is catalyzed in the fischer-tropsch synthesis reactor, the catalyst is replenished according to the conversion rate of the synthesis gas in the fischer-tropsch synthesis reactor.
In the above method, when the equilibrium catalyst is catalyzed in the fischer-tropsch synthesis reactor, the catalyst is supplemented to make the mol percentage of the synthesis gas converted in the fischer-tropsch synthesis reactor less than or equal to 46%, preferably 30 to 46%, and more preferably 10 to 30%.
In the method, the mass percentage of the catalyst in the first stage of the Fischer-Tropsch synthesis reactor for catalyzing the conversion of the synthesis gas is more than 46%.
In the method, when the reactor is a 2-stage fischer-tropsch synthesis reactor connected in series and the flow direction of the synthesis gas and the flow direction of the catalyst are cocurrent, the first stage fischer-tropsch synthesis reactor along the synthesis gas inlet direction is a main reactor, and the later stage is an auxiliary reactor; the mole percent of catalytic synthesis gas conversion in the main reactor is more than 46 percent, and the mole percent of synthesis gas conversion in the auxiliary reactor is less than or equal to 46 percent;
when the reactor is a Fischer-Tropsch synthesis reactor with 2 stages connected in series and the flow direction of the synthesis gas and the flow direction of the catalyst are in a counter-current manner, the Fischer-Tropsch synthesis reactor at the first stage along the entry direction of the synthesis gas is a pre-reaction system, and the Fischer-Tropsch synthesis reactor at the later stage is a main reaction system; the molar percentage of syngas conversion in the pre-reaction system is less than or equal to 46%, and the molar percentage of catalytic syngas conversion in the main reaction system is greater than 46%.
In the above method, the conditions of the fischer-tropsch synthesis reaction are as follows: the temperature can be 180-380 ℃, and the pressure can be 0.5-6.0 MPaG;
the catalyst is a Fischer-Tropsch catalyst capable of generating Fischer-Tropsch synthesis reaction.
In the above process, the catalyst is selected from iron-based and/or cobalt-based catalysts, preferably iron-based catalysts.
In the method, the tail gas synthesized by each stage of Fischer-Tropsch synthesis reactor is sent to the next stage of Fischer-Tropsch synthesis reactor, and is discharged out of the system from the last stage of Fischer-Tropsch synthesis reactor.
In the above method, the reaction tail gas of each stage of the Fischer-Tropsch synthesis reactor generates CO due to the water gas shift reaction2Removal is carried out in each stage of the Fischer-Tropsch synthesis reactor.
When the flow direction of the synthesis gas and the flow direction of the catalyst are in counter-flow, the method has the following advantages: 1) the catalyst still having higher activity after passing through the main reaction section can continue to react in the pre-reaction section until the activity is reduced to a certain degree and then is discharged out of the system as a waste catalyst, so that the utilization rate of the catalyst can be obviously improved, and the cost of the catalyst can be reduced;
2) the catalyst after reaction is adopted for pre-reaction, so that the influence of sulfur in the fresh synthesis gas on the fresh catalyst can be avoided, and the poisoning risk of the catalyst is reduced;
3) the catalyst after reaction is used for pre-reaction, so that a part of fresh gas is pre-reacted, and generated water is discharged from a gas phase, thereby reducing the effective gas partial pressure entering a normal reaction section, reducing the strength of a second-stage reaction, reducing the inactivation of the fresh catalyst caused by higher water content, and prolonging the service life of the catalyst.
When the flow direction of the synthesis gas and the flow direction of the catalyst are cocurrent, the method has the following advantages:
1. the catalyst still having higher activity after passing through the main reaction section can continue to react in the pre-reaction section until the activity is reduced to a certain degree and then is discharged out of the system as a waste catalyst, so that the utilization rate of the catalyst can be obviously improved, and the cost of the catalyst can be reduced;
2. the catalyst after reaction is used for pre-reaction, so that a part of fresh gas is pre-reacted, and generated water is discharged from a gas phase, thereby reducing the effective gas partial pressure entering a normal reaction section, reducing the strength of a second-stage reaction, reducing the inactivation of the fresh catalyst caused by higher water content, and prolonging the service life of the catalyst.
Drawings
FIG. 1 is a schematic diagram of an example of a countercurrent cascade Fischer-Tropsch synthesis reaction method of the present invention.
FIG. 2 is a diagram showing an example of a parallel-flow cascade Fischer-Tropsch synthesis reaction method of the present invention.
The individual labels in the figure are as follows:
1, fresh synthesis gas; 2 tail gas consisting of unreacted synthesis gas and gaseous products; 3, reaction tail gas; 4, fresh catalyst; 5 an equilibrium catalyst; 6, a waste catalyst; 7, water; 8 hydrocarbons; 9 pre-reactor (also called auxiliary reactor); 10 main reactor.
Detailed Description
The contents of the present invention are further explained in the following embodiments with reference to the accompanying drawings.
The following examples are described with reference to a preferred countercurrent two-stage Fischer-Tropsch synthesis scheme, preferably with two stages being the main reaction zone and one stage being the pre-reaction zone, and with the pre-reaction zone and the main reaction zone each having only one reactor, and are referred to as the pre-reactor and the main reactor.
Example 1 countercurrent two-stage Fischer-Tropsch Synthesis
FIG. 1 shows a flow chart of a countercurrent cascade Fischer-Tropsch synthesis reaction method. The invention relates to a countercurrent two-stage Fischer-Tropsch synthesis method, which consists of a pre-reactor 9 and a main reactor 10. Fresh catalyst 4 is first fed to a slurry bed reactor or a fluidized bed reactor in the main reactor 10. The equilibrium catalyst 5 which is discharged from the main reactor and has high activity after a period of reaction is added into the pre-reactor 9 of the previous stage to continue the Fischer-Tropsch synthesis reaction, wherein the reactor can be a slurry bed reactor or a fluidized bed reactor. The catalyst in the pre-reactor 9 is less active than the main reactor and after a period of reaction, the equilibrium catalyst in the reactor is discharged from the system as spent catalyst 6.
The trace sulfur contained in the fresh synthesis gas 1 is mainly deposited on the waste catalyst discharged from the pre-reactor after reaction, so that the sulfur content of the fresh catalyst is ensured to be lower, and higher conversion rate can be maintained.
Example 2 Co-current two-stage Fischer-Tropsch Synthesis
The present example is further explained with reference to fig. 2, and is described below in terms of a co-current two-stage fischer-tropsch synthesis scheme, preferably with one stage being the primary reaction zone and the second stage being the secondary reaction zone, and assuming that there is only one reactor for each of the primary and secondary reaction zones, and is referred to as the primary reactor 10 and the secondary reactor 9.
The parallel-flow two-stage Fischer-Tropsch synthesis method comprises a main reaction section 10 and an auxiliary reactor 9. Fresh catalyst 4 is first added to the slurry or fluidized bed reactor in the main reaction 10. The equilibrium catalyst 5 discharged from the main reactor 10 after a certain period of reaction still has high activity, and is added into the auxiliary reactor 9 of the next stage to continue the Fischer-Tropsch synthesis reaction, wherein the reactor can be a slurry bed reactor or a fluidized bed reactor. The catalyst in the pre-reactor is less active than the main reactor 10 and after a period of reaction, the equilibrium catalyst in the reactor is discharged from the system as spent catalyst 6.
For the parallel-flow cascade reaction, the trace amount of sulfur contained in the fresh synthesis gas 1 may cause the deactivation of the main reactor catalyst, so that the sulfur content must be at least less than 25ppb, which is a high requirement for the desulfurization capability of the front system.
Comparative examples 1,
A single-stage main reactor was used for the Fischer-Tropsch synthesis as a comparative example of the present invention.
Synthesis gas from a synthesis gas production unit, H2the/CO is 1.85, the mixed solution enters a main reactor to carry out Fischer-Tropsch synthesis reaction, and a precipitated Fe-based catalyst (produced by Zhongke synthetic oil technology Co., Ltd.) is adopted. The internal circulation ratio was 1.5, and the decarburization circulation ratio was 0.2.
Fresh catalyst is added into the main reactor according to a certain period and proportion, for example, one batch is replaced every 10 days, and the replacement amount of each batch is 5 percent of the retained amount of the catalyst. The average oil yield of the catalyst in the main reactor was 1600 tons oil/ton catalyst, and the total conversion of syngas package was 93%.
When a small amount of sulfur (e.g., 0.2ppm) in the syngas causes catalyst poisoning, the overall catalyst oil yield drops to 800 tons of oil per ton of catalyst, with a total syngas package conversion of 80%.
Examples 3,
The process scheme shown in fig. 1 is adopted to test the working condition that the pre-reactor and the main reactor are both slurry bed reactors, and the inactivation analysis of the catalyst is carried out according to the activity change trend of the catalyst in an actual factory, and compared with the single-stage working condition without the counter-current reaction.
Synthesis gas from a synthesis gas production unit, H2the/CO is 1.85, firstly enters a pre-reactor, and the Fischer-Tropsch synthesis reaction is carried out by adopting a precipitated Fe-based catalyst produced by the technical company Limited of Chinese-medicinal synthetic oil. The reaction section is not provided with a decarbonization unit (CO generated by the reaction in the tail gas is removed)2) The internal recycle ratio is about 0.5, i.e. the ratio of reaction off-gas to fresh gas is 0.5, which can be reduced to 0 by testing. And tail gas of the pre-reaction section enters a main reaction section for reaction, the same precipitated Fe-based catalyst is adopted for Fischer-Tropsch synthesis reaction, the tail gas decarburization is arranged in the main reaction section, the internal circulation ratio is 1, and the decarburization circulation ratio is 0.2, namely the ratio of the decarburization return gas to the second-section raw gas is 0.2.
Fresh catalyst is added into the main reactor according to a certain period and proportion (the same replacement proportion and period as those of comparative example 1), and the equilibrium catalyst after reaction is removed according to the same period and proportion and is added into the pre-reactor. The initial values of the catalyst holding amounts (the total amount of the catalyst in the reactor) of the main reactor and the pre-reactor are the same, the replacement frequency proportion is also the same, and the catalyst holding amounts are gradually adjusted along with the reaction.
The results show that the average oil yield of the catalyst in the main reactor is slightly increased to 1700 tons of oil/ton of catalyst, and even if the average oil yield of the catalyst in the pre-reactor is reduced to 600 tons of oil/ton of catalyst (the lowest limit), the target of 34 percent conversion in the pre-reactor and 64 percent conversion in the main reactor can be realized. Comprehensively considering, the actual oil yield of the catalyst reaches 2500 tons of oil per ton of catalyst, and the using amount of the catalyst is obviously reduced. The total conversion of the synthesis gas increased to 98% and the conversion of CO approached 100%. When the synthesis gas contains a small amount of sulfur (such as 0.2ppm), the activity of the catalyst in the pre-reactor is reduced to about 800 tons of oil/ton of catalyst, the activity of the catalyst in the main reactor is not affected, and the actual oil yield of the catalyst can still be maintained at the level of 2500 tons of oil/ton of catalyst. The conversion rate of the total package of the synthetic gas is not obviously changed. Compared with the comparative example 1, the whole device has the advantages that the pre-reaction section does not need to be provided with the internal circulation and the decarburization circulation, the circulation ratio of the main reaction section is reduced, and the operation power consumption is reduced.
Examples 4,
By adopting the process scheme shown in FIG. 2, the working conditions that the main reactor and the auxiliary reactor are slurry bed reactors are tested, and the inactivation analysis of the catalyst is carried out according to the activity change trend of the catalyst in the actual plant, and compared with the single-stage working condition without parallel flow reaction.
Synthesis gas from a synthesis gas production unit, H2the/CO is 1.85, firstly enters a main reactor, and the Fischer-Tropsch synthesis reaction is carried out by adopting a precipitated Fe-based catalyst produced by the Chinese-medicinal oil technology company Limited. The main reaction section is provided with an exhaust gas decarburization cycle, the internal recycle ratio is 1.3, and the decarburization recycle ratio is 0.2, namely the ratio of the decarburization return gas to the second-stage raw material gas is 0.2. The tail gas of the main reaction section enters an auxiliary reaction section which is not provided with a decarburization unit (CO generated by the reaction in the tail gas is removed)2) The internal recycle ratio was about 0.5, i.e. the ratio of reaction off-gas to fresh gas was 0.5. And the synthetic tail gas at the second-stage outlet enters a decarburization unit for decarburization and then is treated by removing tail gas.
Fresh catalyst is added into the main reactor according to a certain period and proportion (the same replacement proportion and period as those of comparative example 1), and the equilibrium catalyst after reaction is removed according to the same period and proportion and is added into the auxiliary reactor. The initial values of the catalyst holding amounts (the total amount of the catalyst in the reactor) of the main reactor and the auxiliary reactor are the same, the replacement frequency proportion is also the same, and the catalyst holding amounts are gradually adjusted along with the reaction.
The results show that the average oil yield of the catalyst in the main reactor is slightly increased to 1600 tons of oil per ton of catalyst, and even if the average oil yield of the catalyst in the auxiliary reactor is reduced to 400 tons of oil per ton of catalyst (the lowest limit), the target of 74 percent conversion in the main reactor and 24 percent conversion in the auxiliary reactor can be realized. Comprehensively considering, the actual oil yield of the catalyst reaches 2100 tons of oil/ton of catalyst, and the dosage of the catalyst is obviously reduced. The total conversion of the synthesis gas increased to 97.5%, and the conversion of CO approached 100%. When the synthesis gas contains a small amount of sulfur (e.g. 0.2ppm), the catalyst activity in the main reactor is reduced to about 800 tons of oil/ton of catalyst, the catalyst activity in the auxiliary reactor is reduced in the same proportion, the actual oil yield of the catalyst can still be maintained at 400 tons of oil/ton of catalyst, and the oil yield of the catalyst in the overall process is reduced to the level of 1000 tons of oil/ton of catalyst. The total package syngas conversion rate drops to 83%. Compared with the comparative example 1, the whole device has the advantages that the circulation ratio of the main reaction section is reduced, the inner circulation and the decarburization circulation are not needed in the auxiliary reaction section, and the operation power consumption is reduced.
Comparative examples 2,
A single-stage main reactor was used for the Fischer-Tropsch synthesis reaction, and a fixed fluidized bed reactor was used as a comparative example of example 4 of the present invention.
Synthesis gas from a synthesis gas production unit, H2the/CO is 1.50, the catalyst enters a main reactor to carry out Fischer-Tropsch synthesis reaction, and a fused Fe-based catalyst produced by Chinese-medicinal oil technology Limited is adopted. The internal circulation ratio was 1.0, and the decarburization circulation ratio was 0.3.
Fresh catalyst is added into the main reactor according to a certain period and proportion, for example, one batch is replaced every 15 days, and the replacement amount of each batch is 2 percent of the catalyst retention amount. The average oil yield of the catalyst in the main reactor was 1200 tons oil/ton catalyst and the total package conversion of syngas was 90%.
When a small amount of sulfur (e.g., 0.2ppm) in the syngas causes catalyst poisoning, the overall catalyst oil yield drops to 600 tons of oil per ton of catalyst, with a total syngas package conversion of 78%.
Examples 5,
The process scheme shown in fig. 1 is adopted to test the working conditions that the pre-reactor and the main reactor are both fixed fluidized beds, and the inactivation analysis of the catalyst is carried out according to the activity change trend of the catalyst in the actual factory, and compared with the single-stage working condition without the counter-current reaction.
Synthesis gas from a synthesis gas production unit, H2the/CO is 1.50, firstly enters a pre-reactor, and carries out Fischer-Tropsch synthesis reaction by adopting a molten Fe-based catalyst produced by the technical company Limited of Chinese-Korea synthetic oil. The reaction section is not provided with a decarbonization unit (CO generated by the reaction in the tail gas is removed)2) The internal recycle ratio is about 1.0, namely the ratio of the reaction tail gas to the fresh gas is 0.5, and tests show that the internal recycle ratio can be reduced to 0. And tail gas of the pre-reaction section enters a main reaction section for reaction, the same molten Fe-based catalyst is adopted for Fischer-Tropsch synthesis reaction, the tail gas is decarbonized in the section, the internal circulation ratio is 0.75, and the decarbonization circulation ratio is 0.2, namely the ratio of the decarbonized return gas to the second-section raw gas is 0.2.
Fresh catalyst is added into the main reactor according to a certain period and proportion (the same replacement proportion and period as the comparative example 2), and the equilibrium catalyst after reaction is removed according to the same period and proportion and is added into the pre-reactor. The initial values of the catalyst holding amounts (the total amount of the catalyst in the reactor) of the main reactor and the pre-reactor are the same, the replacement frequency proportion is also the same, and the catalyst holding amounts are gradually adjusted along with the reaction.
The results show that the average oil yield of the catalyst in the main reactor is slightly increased to 1300 tons of oil/ton of catalyst, and even if the average oil yield of the catalyst in the pre-reactor is reduced to 400 tons of oil/ton of catalyst (the lowest limit), the target of 34 percent conversion in the pre-reactor and 64 percent conversion in the main reactor can be realized. Comprehensively considering, the actual oil yield of the catalyst reaches 1900 tons of oil/ton of catalyst, and the dosage of the catalyst is obviously reduced. The total conversion rate of the synthesis gas is increased to 96%, and the conversion rate of CO is close to 99%. When the synthesis gas contains a small amount of sulfur (such as 0.2ppm), the activity of the catalyst in the pre-reactor is reduced to about 600 tons of oil/ton of catalyst, the activity of the catalyst in the main reactor is not affected, and the actual oil yield of the catalyst can still be maintained at the level of 1900 tons of oil/ton of catalyst. The conversion rate of the total package of the synthetic gas is not obviously changed. Compared with the comparative example 2, the whole device has the advantages that the pre-reaction section does not need to be provided with the internal circulation and the decarburization circulation, the circulation ratio of the main reaction section is reduced, and the operation power consumption is reduced.
Examples 6,
The process scheme shown in fig. 2 is adopted to test the working conditions of the main reactor and the auxiliary reactor which are both fixed fluidized beds, and the inactivation analysis of the catalyst is carried out according to the activity change trend of the catalyst in the actual plant, and compared with the single-stage working condition without the counter-current reaction.
The reactor form of this example employed a fixed fluidized bed, and the reaction conditions were the same as in comparative example 2 and example 5, except that the reaction process was the same as in example 3.
The results show that the average oil yield of the catalyst in the main reactor is slightly increased to 1300 tons of oil/ton of catalyst, and the average oil yield of the catalyst in the auxiliary reactor can achieve the target of 70% conversion in the main reactor and 26% conversion in the auxiliary reactor even if the average oil yield of the catalyst in the auxiliary reactor is reduced to 300 tons of oil/ton of catalyst (the lowest limit). Comprehensively considering, the actual oil yield of the catalyst reaches 1450 tons of oil/ton of catalyst, and the using amount of the catalyst is obviously reduced. The total conversion of the synthesis gas increased to 95.5%, and the conversion of CO approached 98.5%. When the synthesis gas contains a small amount of sulfur (e.g. 0.2ppm), the catalyst activity in the main reactor is reduced to about 600 tons of oil/ton of catalyst, the catalyst activity in the auxiliary reactor is reduced in the same proportion, the actual oil yield of the catalyst can still be maintained at 300 tons of oil/ton of catalyst, and the oil yield of the catalyst in the overall process is reduced to the level of 700 tons of oil/ton of catalyst. The total package syngas conversion rate drops to 75%. Compared with the comparative example 2, the whole device has the advantages that the circulation ratio of the main reaction section is reduced, the inner circulation and the decarburization circulation can be omitted for assistance, and the operation power consumption is reduced.
Example 7,
The process scheme shown in fig. 1 is adopted to test the working condition that the pre-reactor and the main reactor are both slurry bed reactors, and the inactivation analysis of the catalyst is carried out according to the activity change trend of the catalyst in an actual factory, and compared with the single-stage working condition without the counter-current reaction.
The synthesis gas from the synthesis gas production unit, H2/CO is 1.85, firstly enters a pre-reactor, and is subjected to Fischer-Tropsch synthesis reaction by adopting a precipitated Fe-based catalyst produced by Zhongke synthetic oil technology Limited. The reaction section is not provided with a decarbonization unit (for removing CO2 generated in the reaction in the tail gas), and the internal circulation ratio is about 0.5, namely the ratio of the reaction tail gas to the fresh gas is 0.5, and the internal circulation ratio can be reduced to 0 through tests. And tail gas of the pre-reaction section enters a main reaction section for reaction, the same precipitated Fe-based catalyst is adopted for Fischer-Tropsch synthesis reaction, the tail gas decarburization is arranged in the main reaction section, the internal circulation ratio is 1, and the decarburization circulation ratio is 0.2, namely the ratio of the decarburization return gas to the second-section raw gas is 0.2.
Fresh catalyst is added into the main reactor according to a certain period and proportion (the same replacement proportion and period as those of comparative example 1), and the equilibrium catalyst after reaction is removed according to the same period and proportion and is added into the pre-reactor. The initial values of the catalyst holding amounts (the total amount of the catalyst in the reactor) of the main reactor and the pre-reactor are the same, the replacement frequency proportion is also the same, and the catalyst holding amounts are gradually adjusted along with the reaction.
The results show that the average oil yield of the catalyst in the main reactor is slightly increased to reach 1700 tons of oil/ton of catalyst, and even if the average oil yield of the catalyst in the pre-reactor is reduced to 1350 tons of oil/ton of catalyst (the lowest limit), the target of 46 percent conversion in the pre-reactor and 54 percent conversion in the main reactor can be realized. Comprehensively considering, the actual oil yield of the catalyst reaches 3000 tons of oil/ton of catalyst, and the dosage of the catalyst is obviously reduced. The total conversion rate of the synthesis gas is increased to 99.5%, and the conversion rate of CO is close to 100%. When the synthesis gas contains a small amount of sulfur (such as 0.2ppm), the activity of the catalyst in the pre-reactor is reduced to about 800 tons of oil/ton of catalyst, the activity of the catalyst in the main reactor is not affected, and the level of 2600 tons of oil/ton of catalyst with the actual oil yield of the catalyst can still be maintained. The conversion rate of the total package of the synthetic gas is not obviously changed. Compared with the comparative example 1, the whole device has the advantages that the pre-reaction section does not need to be provided with the internal circulation and the decarburization circulation, the circulation ratio of the main reaction section is reduced, and the operation power consumption is reduced.
Claims (10)
1. A method for cascade Fischer-Tropsch synthesis reaction comprises the following steps: containing CO and H2The synthesis gas is catalyzed by a catalyst to carry out Fischer-Tropsch synthesis reaction when sequentially passing through a plurality of stages of Fischer-Tropsch synthesis reactors connected in series, and hydrocarbon products and water generated by each stage of Fischer-Tropsch synthesis reactor are separated independently and then are merged and discharged out of the system;
wherein the flow direction of the synthesis gas and the flow direction of the catalyst are cocurrent and/or countercurrent;
1) when the flow direction of the synthesis gas and the flow direction of the catalyst are in parallel flow, along the flow direction of the synthesis gas, the catalyst enters from the first-stage Fischer-Tropsch synthesis reactor and replaces an equilibrium catalyst, and the equilibrium catalyst continuously catalyzes the Fischer-Tropsch synthesis reaction in the next-stage Fischer-Tropsch synthesis reactor until the catalyst is discharged from the last-stage Fischer-Tropsch synthesis reactor;
2) and when the flow direction of the synthesis gas is countercurrent to the flow direction of the catalyst, replacing the equilibrium catalyst by the catalyst after the catalyst enters from the last stage of the Fischer-Tropsch synthesis reactor against the flow method of the synthesis gas, and continuously catalyzing the Fischer-Tropsch synthesis reaction in the previous stage of the Fischer-Tropsch synthesis reactor by the equilibrium catalyst until the catalyst is discharged from the first stage of the Fischer-Tropsch synthesis reactor.
2. The method of claim 1, wherein: the Fischer-Tropsch synthesis reactor in the multistage series connection is a Fischer-Tropsch synthesis reactor in the 2-stage series connection.
3. The method of claim 2, wherein: each stage of Fischer-Tropsch synthesis reactor is one or more slurry bed reactors and/or fluidized bed reactors connected in parallel; when the flow direction of the synthesis gas and the flow direction of the catalyst are in parallel flow, the number of the slurry bed reactors and/or the fluidized bed reactors connected in parallel in the Fischer-Tropsch synthesis reactor at the next stage is less than or equal to that of the previous stage; when the flow direction of the synthesis gas and the flow direction of the catalyst are in counter current, the number of the slurry bed reactors and/or the fluidized bed reactors connected in parallel in the Fischer-Tropsch synthesis reactor at the later stage is more than or equal to that of the previous stage
The fluidized bed reactor is specifically a circulating fluidized bed reactor and/or a fixed fluidized bed reactor.
4. The method according to any one of claims 1-3, wherein: and when the equilibrium catalyst is catalyzed in the Fischer-Tropsch synthesis reactor, replenishing the catalyst according to the conversion rate of the synthesis gas in the Fischer-Tropsch synthesis reactor.
5. The method according to any one of claims 1-4, wherein: and when the equilibrium catalyst is catalyzed in the Fischer-Tropsch synthesis reactor, supplementing the catalyst to ensure that the mol percentage of the synthesis gas converted in the Fischer-Tropsch synthesis reactor is less than or equal to 46%.
6. The method according to any one of claims 1-5, wherein: the catalyst catalyzes the conversion of the synthesis gas in the first stage of the Fischer-Tropsch synthesis reactor to a molar percentage of more than 46 percent.
7. The method according to any one of claims 1-5, wherein: the conditions of the Fischer-Tropsch synthesis reaction are as follows: the temperature is 180-380 ℃, and the pressure is 0.5-6.0 MPaG;
the catalyst is a Fischer-Tropsch catalyst capable of generating Fischer-Tropsch synthesis reaction.
8. The method according to any one of claims 1-7, wherein: the catalyst is selected from iron-based and/or cobalt-based catalysts, preferably iron-based catalysts.
9. The method according to any one of claims 1-8, wherein: in the method, tail gas synthesized by each stage of Fischer-Tropsch synthesis reactor is sent to the next stage of Fischer-Tropsch synthesis reactor, and is discharged out of the system from the last stage of Fischer-Tropsch synthesis reactor.
10. The method according to any one of claims 1-9, wherein: CO in reaction tail gas of each stage of the Fischer-Tropsch synthesis reactor2Removal is carried out in each stage of the Fischer-Tropsch synthesis reactor.
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| CN112625727A (en) * | 2020-11-29 | 2021-04-09 | 上海兖矿能源科技研发有限公司 | Series system for Fischer-Tropsch synthesis |
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