System and method for directly preparing olefin from synthesis gas through step-by-step conversion coupling segmented temperature control

Abstract

The invention provides a system and method for directly preparing olefin from synthesis gas through step-by-step conversion coupling and segmented temperature control, and the system comprises a fluidized bed reactor which is filled with a fluidized bed catalyst and is used for catalytically converting at least a first part of synthesis gas into product gas; the fixed bed reactor is filled with a fixed bed catalyst, is communicated with the fluidized bed reactor and is used for receiving the product gas and the rest of the synthesis gas, so that at least a second part of the synthesis gas is catalytically converted into the product gas, and deep conversion of the synthesis gas is realized; wherein the fixed bed reactor internally comprises a cooling section and a heating section which are communicated with each other, the cooling section is communicated with the fluidized bed reactor, the cooling section is used for reducing the reaction temperature of the synthesis gas in the fixed bed reactor in the early reaction stage, and the heating section is used for increasing the reaction temperature of the synthesis gas in the fixed bed reactor in the later reaction stage. According to the system provided by the invention, the problem that high conversion rate and high heat exchange efficiency are difficult to consider in the traditional process of preparing olefin from synthesis gas is solved.

Description

Technical Field

[0001] The present application relates to the technical field of directly preparing olefins from syngas, and particularly relates to a system and method for directly preparing olefins from syngas by stepwise conversion coupling with segmented temperature control. Background Art

[0002] Directly preparing olefins from syngas (CO and H2) is a method of directly converting raw materials such as coal, natural gas, and biomass into high-value olefin products through syngas in one step. It has the advantages of short process flow, high energy efficiency, strong raw material adaptability, and high olefin selectivity under catalyst regulation. In recent years, it has become a hot research and industrialization direction in the field of olefin preparation.

[0003] In the actual process of preparing olefins from syngas, early research mostly used modified iron-based catalyst systems, enabling the single-pass conversion rate of CO to exceed 95%, effectively reducing the gas separation and gas circulation loads. However, the process of directly preparing olefins from this syngas is essentially a coupling of two highly exothermic reaction stages, namely preparing methanol from syngas and preparing olefins from methanol, in the same reactor. This intense exothermic characteristic of the essentially coupled exothermic reaction poses a severe challenge to reactor design.

[0004] Currently, this process mostly uses fixed-bed reactors or fluidized-bed reactors as the core reaction units. Since strong exothermic reactions occur in the same reactor, for fixed-bed reactors, they have the advantages of long gas residence time and high conversion rate, but the engineering challenges of heat exchange are too great, easily causing the fixed-bed reactor to run away in temperature. Olefins will undergo secondary hydrogenation and become inert and low-value alkanes, reducing product selectivity and economy. For fluidized-bed reactors, although the problem of reactor runaway in temperature can be inhibited to a certain extent by increasing the gas velocity and enhancing the gas-solid turbulence degree to achieve efficient indirect heat exchange, increasing the gas velocity will shorten the gas-solid contact time and reduce the syngas conversion rate. At the same time, the gas-solid contact state in the fluidized-bed reactor is close to the complete mixing flow state, and the syngas conversion rate is generally significantly lower than that of the fixed-bed reactor, making it difficult to achieve a high one-time conversion rate.

[0005] Therefore, the actual process of directly preparing olefins from syngas still faces key engineering problems in terms of reactor thermal management and the balance of deep syngas conversion. Summary of the Invention

[0006] Aiming at the above problems, one of the objectives of the present invention is to provide a system for directly preparing olefins from syngas by stepwise conversion coupling with segmented temperature control to solve the problem of being difficult to balance high conversion rate and high heat exchange efficiency during the preparation of olefins. Another objective of the present invention is to provide a method for directly preparing olefins from syngas by stepwise conversion coupling with segmented temperature control.

[0007] To achieve one of the objectives, in a first aspect, the present invention provides a system for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control. The technical solution adopted is as follows: A system for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control, the system comprising: A fluidized bed reactor filled with a fluidized bed catalyst and syngas inside, for catalytically converting at least a first portion of the syngas into product gas; A fixed bed reactor connected to the fluidized bed reactor, for receiving the product gas and the remaining portion of the syngas; the fixed bed reactor is filled with a fixed bed catalyst inside, for catalytically converting at least a second portion of the syngas into product gas to achieve deep conversion of the syngas; Wherein, the fixed bed reactor includes a cooling section and a heating section that are interconnected, and the cooling section is connected to the fluidized bed reactor. The cooling section is used to reduce the reaction temperature of the syngas in the fixed bed reactor in the early stage of the reaction, and the heating section is used to increase the reaction temperature of the syngas in the fixed bed reactor in the later stage of the reaction.

[0008] As one of the preferred solutions, the system further includes a partition plate provided with a plurality of air holes; the partition plate is disposed inside the fixed bed reactor to divide the fixed bed reactor into the cooling section and the heating section that are connected through the air holes.

[0009] As one of the preferred solutions, the partition plate is radially disposed inside the fixed bed reactor so that the cooling section is located above the heating section.

[0010] As one of the preferred solutions, the system further includes: A fluidized bed cooler disposed inside the fluidized bed reactor and filled with a first cooling medium; A fixed bed cooler disposed inside the cooling section and filled with a second cooling medium; A fixed bed heater disposed inside the heating section.

[0011] As one of the preferred solutions, the fixed bed heater is filled with a heating medium; wherein, the fluidized bed cooler is connected to the fixed bed heater so that after the first cooling medium absorbs the heat released during the conversion of the syngas in the fluidized bed reactor, it serves as the heating medium in the fixed bed heater.

[0012] As one of the preferred solutions, the content of the first portion of the syngas is 75% - 95% of the total content of the syngas; the content of the second portion of the syngas is 5% - 25% of the total content of the syngas.

[0013] To achieve the second object, in a second aspect, the present invention provides a method for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control. The technical solution adopted is as follows: A method for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control, the method comprising: Introduce syngas or hydrogen into the fluidized bed reactor and the fixed bed reactor to reduce the fluidized bed catalyst loaded in the fluidized bed reactor and the fixed bed catalyst loaded in the fixed bed reactor; After the catalytic reduction is completed, introduce syngas into the fluidized bed reactor, and introduce a first cooling medium into the fluidized bed cooler in the fluidized bed reactor, and control the temperature in the fluidized bed reactor to be 320°C - 370°C, so that at least the first part of the syngas is catalytically converted into product gas by the fluidized bed catalyst; Use the cooling section of the fixed bed reactor to receive the product gas and the remaining part of the syngas, introduce a second cooling medium into the fixed bed cooler in the cooling section, and control the temperature of the syngas entering the fixed bed reactor in the early stage of the reaction to be 320°C - 340°C; Use the heating section of the fixed bed reactor to receive the product gas and the unconverted syngas transmitted by the cooling section, and introduce a heating medium into the fixed bed heater in the heating section, and control the temperature of the syngas entering the fixed bed reactor in the later stage of the reaction to be 280°C - 300°C; Use the cooling section and the heating section to continue catalytically convert at least the second part of the syngas into product gas by the fixed bed catalyst during different temperature periods, so as to achieve the deep conversion of the syngas.

[0014] As one of the preferred solutions, the introducing the heating medium into the fixed bed heater in the heating section includes: Use the fixed bed heater to receive the first cooling medium that absorbs the heat released by the catalytic conversion reaction in the fluidized bed cooler, and use the heated first cooling medium as the heating medium.

[0015] As one of the preferred solutions, both the fluidized bed catalyst and the fixed bed catalyst include active components and promoters; wherein, the active components include one or more of metal carbides, metal phosphates, and metal borates; the promoters include one or more of carbonates, chlorides, and nitrates of potassium, sodium, calcium, and magnesium.

[0016] As one of the preferred solutions, the fluidized bed catalyst further includes porous carbon, and the active components and the promoters are loaded on the porous carbon; or, The fixed-bed catalyst further includes a carrier, which includes one or more of carbon nanotubes, graphene, alumina, silica, and thorium oxide; the active component and the promoter are loaded on the carrier.

[0017] Compared with the prior art, the present application has the following advantages: Compared with a single fixed-bed conversion process, the overall heat transfer coefficient of the fluidized bed reactor used in the present invention is large, which can effectively reduce the total heat exchange area by 80%-90%. Compared with a single fluidized bed conversion process, when the same conversion rate is achieved at the outlet, the present invention can save 50%-70% of the catalyst loading amount and 50%-90% of the reactor volume. By adopting the system provided by the embodiments of the present invention, it is possible to ensure effective heat exchange during the direct synthesis of olefins from syngas with strong exothermic reactions, suppress reactor runaway temperature, control the selectivity of olefin products, and control extremely high conversion rates, reduce the gas circulation volume and the difficulty of gas separation; it is also possible to compensate for heat and improve the catalyst activity through the heating section in the later stage of the reaction, maintain the reaction temperature, adapt to the heat load fluctuations with gradually decreasing heat release along the process in the one-step reaction system, avoid a decrease in the conversion rate in the later stage or even "flameout" of the reaction, and further reduce the catalyst loading amount in the fixed bed by 30%. It has the advantages of continuous operation and low cost.

[0018] The advantages of the method relative to the prior art are the same as those of the above system and will not be elaborated here. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions of the present application, the drawings required for the description of the present application will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is a structural framework diagram of a system for directly preparing olefins from syngas with step-by-step conversion coupling and segmented temperature control according to an embodiment of the present application; Figure 2 It is a step flow chart of a method for directly preparing olefins from syngas with step-by-step conversion coupling and segmented temperature control according to an embodiment of the present application.

[0021] Description of the Reference Numerals: 1. Fluidized bed reactor; 2. Cooling section; 3. Heating section; 4. Baffle; 5. Fluidized bed cooler; 6. Fixed bed heater; 7. Fixed bed cooler. Detailed Description of the Embodiments

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with the features of other existing technologies falls within the protection scope of the present invention. Moreover, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present invention.

[0023] In the embodiments, if the specific experimental steps or conditions are not specified, the operations or conditions of the conventional experimental steps described in the existing technologies in the field can be followed. For the reagents and other instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchase. In addition, the accompanying drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus the repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0024] For technologies, methods, and devices known to those of ordinary skill in the relevant fields, detailed discussions may not be made, but under appropriate circumstances, the said technologies, methods, and devices should be regarded as a part of the specification of the present invention.

[0025] In the description of the present invention, it should be understood that using words such as "first" and "second" to limit components is only for the convenience of differentiating the corresponding components. Without further statement, the above words have no special meaning, and thus cannot be construed as limiting the protection scope of the present invention.

[0026] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] It should be noted that different reaction stages in the one-step synthesis of olefins from syngas essentially belong to the same reaction process in the reactor, and different reaction stages proceed synchronously and are coupled with intense heat release in the same reaction system. In related technologies, some people have proposed setting up multiple reactors for olefin synthesis reactions. However, different synthesis reactions are carried out in different reactors, which essentially belongs to the multi-step method for preparing olefins, and the product modulation problem in the olefin preparation process is solved step by step. Due to different reaction processes, an intermediate gas separation link needs to be set between the reactors, resulting in a complex structure and a long reaction process. Therefore, the technical route of preparing the target product step by step with multiple reactors cannot be applied to the process engineering of directly preparing olefins from syngas, which increases complexity and cannot solve the problem of deep conversion of syngas while solving the problem of reactor runaway temperature caused by intense heat release during the one-step synthesis reaction.

[0028] It can also be known that heat exchangers are provided in fixed-bed reactors in current technologies for full-course cooling and heat exchange. However, through the creative work of the inventors, it is found that in the front stage of the fixed bed, that is, in the early stage of the reaction, when the material just enters the fixed bed, due to the large amount of remaining unreacted CO raw materials, the heat generation during the reaction is large, and cooling and heat exchange must be carried out in this stage, otherwise there is still a risk of runaway temperature. In the later stage of the fixed bed, that is, in the later stage of the reaction, the unreacted CO is greatly reduced, and the corresponding heat generation of the reaction decays. When the heat of reaction in this stage is not sufficient to maintain the reaction temperature, the heat exchanger set to avoid runaway temperature in the early stage continues to play a cooling function, which further leads to too low a temperature, insufficient activity of the catalyst in the later stage, and the reaction process is "extinguished". Therefore, there is a change in the temperature range in the one-step reaction system. A single heat exchange method (i.e., full-course cooling or full-course heating) set in the same fixed-bed reactor to avoid runaway temperature cannot cope with the trend of heat release fluctuations along the reaction in the one-step reaction system, making it difficult to ensure the continuity and stability of the reaction.

[0029] In the first aspect, Figure 1 FIG. shows a schematic structural diagram of a system for directly preparing olefins from syngas with step-by-step conversion coupling and segmented temperature control provided by an embodiment of the present invention. The present invention provides a system for directly preparing olefins from syngas with step-by-step conversion coupling and segmented temperature control. As Figure 1 shown, the system includes: a fluidized-bed reactor 1 filled with a fluidized-bed catalyst and syngas inside, which is used to catalytically convert at least a first part of the syngas into product gas; a fixed-bed reactor connected to the fluidized-bed reactor 1, which is used to receive the product gas and the remaining part of the syngas; the fixed-bed reactor is filled with a fixed-bed catalyst inside, which is used to catalytically convert at least a second part of the syngas into product gas to achieve deep conversion of the syngas. Among them, the fixed-bed reactor includes a cooling section 2 and a heating section 3 that are interconnected, and the cooling section 2 is connected to the fluidized-bed reactor 1. The cooling section 2 is used to reduce the reaction temperature of the syngas located in the fixed-bed reactor in the early stage of the reaction, and the heating section 3 is used to increase the reaction temperature of the syngas located in the fixed-bed reactor in the later stage of the reaction. Specifically, in this embodiment, a fluidized-bed reactor 1 and a fixed-bed reactor are connected in series, and a temperature control partition structure of a cooling section 2 and a heating section 3 is arranged in the fixed-bed reactor. Through the idea of relay conversion by a series of reactors, most of the conversion and heat exchange are realized by the fluidized-bed reactor 1 in the initial stage of the reaction; the remaining part of the deep conversion is realized by the fixed-bed reactor in the final stage of the reaction; at the same time, the functions of the fixed-bed reactor are refined to adapt to the heat load fluctuation of the gradually decreasing heat release along the way of the syngas in the final stage of the reaction, realizing the efficient and deep conversion of the raw materials, and greatly reducing the temperature control difficulty of the fixed-bed reactor.

[0030] Specifically, in the first aspect, taking advantage of the better heat transfer performance of the fluidized-bed reactor 1, the syngas is first introduced into the fluidized-bed reactor 1 for the primary reaction to complete 75%-95% of the reaction amount (based on the activity of the fluidized-bed catalyst), realizing efficient heat exchange and uniform temperature control. Then the unconverted syngas (the remaining part of the syngas) and the product gas are introduced into the fixed-bed reactor for the final reaction. Taking advantage of the better deep conversion performance of the fixed-bed reactor, the remaining 5%-25% of the reaction amount (based on the activity of the fixed-bed catalyst) is completed. Therefore, two reactors with different advantages in performance are used to make the syngas react step by step, realizing the step-by-step deep conversion of the syngas while avoiding reactor runaway temperature.

[0031] Among them, the fixed-bed reactor receives the remaining part of the syngas and realizes the conversion of at least the second part of the syngas, and the content of the second part of the syngas is less than or equal to the content of the remaining part of the syngas. The remaining part of the syngas is specifically the unconverted syngas output from the fluidized-bed reactor 1 and entering the fixed-bed reactor. When the second part of the syngas in the fixed-bed reactor is equal to the content of the remaining part of the syngas, the fluidized-bed reactor 1 and the fixed-bed reactor can complete 100% of the CO conversion rate.

[0032] In this embodiment, after the primary reaction of the fluidized-bed reactor 1, the single-pass CO conversion rate reaches 75%-90%, and the olefin selectivity accounts for 70-85% among hydrocarbons with C2 and above. After the final reaction of the fixed-bed reactor, the total single-pass CO conversion rate reaching the outlet of the fixed-bed reactor reaches 95%-98%.

[0033] In a second aspect, the fixed-bed reactor can improve the CO conversion rate at the end of the reaction during the entire reaction process of syngas. For the interior of the fixed-bed reactor, the cooling section 2 is arranged at the inlet, connected to the outlet of the fluidized-bed reactor 1, and receives the product gas and unreacted syngas generated after the primary reaction in the fluidized-bed reactor 1. The concentration of syngas in the cooling section 2 at the inlet of the fixed-bed reactor is still relatively high, and the total amount of reaction heat generated is large, so it is necessary to exchange heat with cooling water. Therefore, the temperature can be controlled through a separate heat exchange device in the cooling section 2, and the reaction temperature in the cooling section 2 is controlled to be 320°C - 340°C, which can reduce the temperature of the syngas that first enters the fixed-bed reactor in the early stage of the reaction, protect the catalyst, and effectively inhibit the risk of temperature runaway caused by intense heat release.

[0034] The outlet of the cooling section 2 is connected to the inlet of the heating section 3, and the outlet of the heating section 3 serves as the outlet of the fixed-bed reactor. The syngas in the cooling section 2 continues to react in the heating section 3 after completing the preliminary reaction to reach the later stage of the reaction, thereby achieving the deep conversion of syngas through the fixed-bed reactor. Since in the later stage of the reaction, the reaction heat is already insufficient to maintain the temperature, and in addition, a large amount of cooling water is still passed, it will accelerate the reduction of catalyst activity and cause the reaction process to "flame out", failing to achieve the purpose of deep conversion. Therefore, the temperature can be controlled through a separate heat exchange device in the heating section 3, and its reaction temperature is controlled to be 280°C - 300°C, which can increase the temperature of the syngas entering the fixed-bed reactor in the later stage of the reaction, compensate for the problem of insufficient heat generation in the later stage of the reaction, and avoid the problems of catalyst activity decline or reaction termination at the end of the reaction due to insufficient heat generation or excessive cooling.

[0035] Therefore, by setting the cooling section 2 and the heating section 3 in segments in the fixed-bed reactor, it is possible to conform to the heat changes along the process in the ultimate reaction process in the one-step reaction system, realize the segmented adjustment of the temperature in the early and later stages of the ultimate reaction process, avoid the problems of "temperature runaway" or "flameout", and thus improve the continuous stability of the reaction and the deep conversion efficiency of syngas.

[0036] It should be explained that in the entire system of directly synthesizing olefins from syngas, the fixed-bed reactor is used as the terminal reactor for the ultimate reaction of syngas in the second stage, and the syngas in the fixed-bed reactor is already in the final stage of the reaction. Therefore, the early and later stages of the reaction referred to in this embodiment are relative to two different stages of the final reaction occurring in the fixed-bed reactor. The early stage of the reaction specifically refers to the early stage when the syngas enters the middle / middle-upper section of the fixed-bed reactor and experiences the most intense heat release in its bed layer. The later stage of the reaction refers to the later stage when the syngas continues to enter the middle-lower / lower section of the fixed-bed reactor from the middle / middle-upper section of the fixed-bed reactor, and the conversion degree of the syngas gradually increases and the heat release intensity significantly decreases.

[0037] In summary, compared with a single fixed-bed conversion process, the overall heat transfer coefficient of the fluidized bed reactor 1 used in the present invention is large, and the total heat exchange area can be effectively reduced by 80%-90%. Compared with a single fluidized bed conversion process, when the same conversion rate is achieved at the outlet, the present invention can save 50%-70% of the catalyst loading amount and 50%-90% of the reactor volume. By using this system, it is possible to ensure effective heat exchange during the strongly exothermic reaction in the process of directly synthesizing olefins from syngas. Without configuring 8 times the steam to dilute the reaction heat, the reactor runaway temperature can be inhibited, the selectivity of olefin products can be controlled, and an extremely high conversion rate can be controlled, reducing the gas circulation volume and the difficulty of gas separation. It can also compensate for heat and improve the catalyst activity through the heating section 3 in the later stage of the reaction, maintain the reaction temperature, adapt to the heat load fluctuation of gradually decreasing heat release along the process in the one-step reaction system, avoid the decrease of the conversion rate in the later stage or even the "flameout" of the reaction, and further reduce the catalyst loading in the fixed bed by 30%. It has the advantages of continuous operation and low cost.

[0038] Preferably, the system further includes a partition plate 4 provided with a plurality of air holes; the partition plate 4 is arranged in the fixed bed reactor to divide the fixed bed reactor into a cooling section 2 and a heating section 3 connected through the air holes.

[0039] In this embodiment, the partition plate 4 with air holes can divide the inside of the fixed bed reactor into a cooling section 2 and a heating section 3, and the cooling section 2 and the heating section 3 are connected through the air holes, ensuring continuous gas flow in the fixed bed reactor while enabling independent temperature control of different reaction sections. Therefore, the product gas and unreacted syngas after the pre-reaction in the cooling section 2 flow to the heating section 3 through a plurality of air holes, and complex heat management can be realized only through the simple structure of the partition plate 4, solving the temperature control problems of easy runaway temperature in the early stage of the reaction and easy "flameout" in the later stage of the reaction caused by uneven heat release along the process in the existing fixed bed reactor.

[0040] In this embodiment, the partition plate 4 divides the cooling section 2 and the heating section 3, and the fixed bed catalysts arranged in the cooling section 2 and the heating section 3 do not communicate with each other. In some embodiments, the types, quantities, and arrangement manners of the fixed bed catalysts arranged in the cooling section 2 and the heating section 3 may be the same or different.

[0041] Furthermore, the partition 4 is radially arranged in the fixed bed reactor so that the cooling section 2 is located above the heating section 3. In this embodiment, the partition 4 of the present invention is radially arranged, so the fixed bed reactor is divided into two upper and lower chambers in the vertical direction, the upper chamber is the cooling section 2, and the lower chamber is the heating section 3, and the gas flow flows naturally from top to bottom to control the temperature in sections. Among them, the gas flow in the fluidized bed reactor 1 usually flows from bottom to top, so the top outlet of the fluidized bed reactor 1 is connected to the top outlet of the fixed bed reactor through a gas pipeline, and can quickly enter the cooling section 2.

[0042] In some embodiments, the distance between the baffle 4 and the top of the fixed bed reactor may be less than, equal to, or greater than the distance between the baffle 4 and the bottom of the fixed bed reactor, that is, the chamber areas of the cooling section 2 and the heating section 3 may be the same or different. For example, the cooling section 2 may occupy the upper section of the fixed bed reactor for cooling, and the heating section 3 may occupy the middle and lower sections of the fixed bed reactor for compensating the temperature rise.

[0043] As a specific explanation of this embodiment, the system also includes: a fluidized bed cooler 5, which is arranged in the fluidized bed reactor 1 and is filled with a first cooling medium; a fixed bed cooler 7, which is arranged in the cooling section 2 and is filled with a second cooling medium; and a fixed bed heater 6, which is arranged in the heating section 3.

[0044] In this embodiment, both the fluidized bed reactor 1 and the fixed bed reactor are provided with heat exchange equipment, and the cooling section 2 and the heating section 3 in the fixed bed reactor are provided with heat exchange equipment separately. The types of heat exchange equipment provided in each area may be the same or different.

[0045] Specifically, the catalytic reaction in the fluidized bed reactor 1 is usually a violent exothermic reaction, and forced cooling must be performed to control the bed temperature. Therefore, the initial state of the first cooling medium filled in the fluidized bed cooler 5 is a low-temperature state, and the first cooling medium is injected to take away a large amount of heat released during the primary reaction, and the temperature is controlled at 320°C-370°C. The catalytic reaction in the cooling section 2 near the inlet of the fixed bed reactor must be forced to cool to control the bed temperature because the concentration of CO and H2 is high in the early stage and the heat release is still violent. Therefore, the initial state of the second cooling medium filled in the fixed bed cooler 7 is a low-temperature state, and the second cooling medium is injected to take away the heat released in the early stage of the ultimate reaction, and the temperature is controlled at 320°C-340°C. The catalytic reaction in the heating section 3 at the middle and lower sections of the fixed bed reactor requires compensation temperature to control the bed temperature due to the reduced CO concentration and insufficient reaction heat release. Therefore, the initial state of the heating medium filled in the fixed bed heater 6 is a high-temperature state, and the heating medium is injected to supplement the heat required in the late stage of the reaction during the ultimate reaction, and the temperature is controlled at 280°C-300°C to promote the deep conversion of the synthesis gas.

[0046] Among them, both the first cooling medium and the second cooling medium can be introduced from the outside. For example, they are both low-temperature water, which becomes water vapor after absorbing heat and flows out of the corresponding area. Both the fluidized bed cooler 5 and the fixed bed cooler 7 can be heat exchange pipes, jackets, heat exchange coil pipes, etc.

[0047] Among them, the fixed bed heater 6 can be an electric heater, which generates heat when powered on to increase the reaction temperature in the heating section 3.

[0048] Preferably, the fixed bed heater 6 is filled with a heating medium; among them, the fluidized cooler is connected to the fixed bed heater 6, so that after the first cooling medium absorbs the heat released during the synthesis gas conversion process in the fluidized bed reactor 1, it serves as the heating medium in the fixed bed heater 6.

[0049] In this embodiment, the fixed bed heater 6 can also be a heat exchange pipe, a jacket or a heat exchange coil pipe, etc. The inlet of the fixed bed heater 6 is connected to the outlet of the fluidized bed cooler 5. The first cooling medium (such as a water medium) absorbs heat and warms up to become water vapor in the fluidized bed cooler 5. The heated high-temperature steam is directly transported into the fixed bed heater 6 without an external heat source. In the fixed bed heater 6, this heat medium serves as a heat source again to provide the heat required for the reaction at the end stage, ensuring that there is a high enough temperature at the fixed bed outlet for in-depth reaction. Thus, the "extra" heat energy in the fluidized bed reactor 1 is transferred to the heating section 3 in the fixed bed reactor that "lacks" heat, realizing internal heat self-balance. Thus, there is no need for an external heating system, reducing energy consumption. At the same time, heat is recycled locally, reducing heat transfer loss and heat dissipation loss, and simplifying the system structure through a set of mutually coupled heat exchange devices.

[0050] Preferably, the inlet of the fixed bed heater 6 is close to the bottom of the fixed bed reactor, that is, the bottom of the heating section 3, and the outlet of the fixed bed heater 6 is far from the bottom of the heating section 3. Thus, the incoming first cooling medium flows from bottom to top, counter-currently exchanging heat with the gas flow entering the heating section 3 from top to bottom in the cooling section 2, thereby improving the heat utilization efficiency.

[0051] Preferably, the content of the first part of the synthesis gas is 75%-95% of the total content of the synthesis gas; the content of the second part of the synthesis gas is 5%-25% of the total content of the synthesis gas. In this embodiment, according to the selected catalyst type, quantity, layout method, and control of reaction time, temperature, pressure, and mass space velocity, etc., first complete 75%-95% of the reaction amount in the fluidized bed reactor 1, so that most of the primary reactions of the synthesis gas are quickly converted into product gas, and the fluidized bed reactor 1 mainly bears the high heat release of the coupled exothermic reaction. Then complete the remaining 5%-25% of the reaction amount in the fixed bed reactor to carry out the in-depth conversion reaction at the end stage and improve the CO conversion rate.

[0052] Correspondingly, for the second aspect, please refer to Figure 2As shown Figure 2 This is a process flow diagram of a method for directly preparing olefins from syngas with step - by - step conversion coupling and segmented temperature control. The present invention also provides a method for directly preparing olefins from syngas with step - by - step conversion coupling and segmented temperature control, which utilizes the system for directly preparing olefins from syngas with step - by - step conversion coupling and segmented temperature control provided in the first aspect of the present invention. This method includes the following steps: S1. Introduce syngas or hydrogen into the fluidized - bed reactor 1 and the fixed - bed reactor to reduce the fluidized - bed catalyst loaded in the fluidized - bed reactor 1 and the fixed - bed catalyst loaded in the fixed - bed reactor; Among them, before the reactor runs, first load the catalysts into the fluidized - bed reactor 1 and the fixed - bed reactor, and reduce them with syngas or H2 at 400°C - 420°C and 2MPa - 3MPa for 1h - 6h to reduce and activate the catalysts loaded in the fluidized - bed reactor 1 and the fixed - bed reactor. The partial pressure of hydrogen or syngas is controlled at 10% - 80%, and the rest is nitrogen, carbon dioxide or methane as inert gas to regulate the reaction atmosphere.

[0053] In this embodiment, both the fluidized - bed catalyst and the fixed - bed catalyst include active components and promoters; among them, the active components include one or more of metal carbides, metal phosphates and metal borates; among them, the metals are iron, cobalt, nickel, etc. The promoter is an alkaline compound, and the promoter includes one or more of carbonates, chlorides and nitrates of potassium, sodium, calcium and magnesium.

[0054] Among them, the mass ratio of the promoter to the active component is 1:(2 - 30).

[0055] Furthermore, the fluidized - bed catalyst further includes porous carbon, and the active components and promoters are loaded on the porous carbon; among them, the mass ratio of the porous carbon is 20% - 50%.

[0056] Or, the fixed - bed catalyst further includes a carrier, and the carrier includes one or more of carbon nanotubes, graphene, alumina, silica and thorium oxide; the active components and promoters are loaded on the carrier. Among them, the mass ratio of the carrier is 30% - 65%.

[0057] S2. After the catalytic reduction is completed, introduce syngas into the fluidized - bed reactor 1, and introduce the first cooling medium into the fluidized - bed cooler 5 in the fluidized - bed reactor 1, and control the temperature in the fluidized - bed reactor 1 to be 320°C - 370°C, so that at least the first part of the syngas is catalytically converted into product gas by the fluidized - bed catalyst; After the catalyst activation treatment, enter the primary reaction stage. Feed the low - temperature syngas at 20°C - 50°C into the fluidized - bed reactor 1. The volume ratio of H2 to CO in the syngas is (1.2 - 2):1, and maintain the mass space velocity during the primary reaction process at 1 - 10h-1 , at a pressure of 2 MPa - 6 MPa, through direct catalytic conversion by a fluidized bed catalyst, 75% - 95% of the reaction amount is completed in the fluidized bed reactor 1, enabling the rapid conversion of the vast majority of the primary synthesis gas reactions to generate product gas. At the same time, cooling water is introduced into the inlet of the fluidized bed cooler 5 in the fluidized bed reactor 1 to cool the catalyst, controlling the temperature at 320°C - 370°C. The cooling water absorbs the heat released during the reaction process in this system and is heated and vaporized into high-temperature steam, flowing out from the outlet of the fluidized bed cooler 5.

[0058] After the primary reaction ends, most of the conversion in the synthesis gas is completed, with the single-pass conversion rate of CO reaching 75% - 90%, and the olefin selectivity accounting for 70% - 85% among hydrocarbons with C2 and above.

[0059] Preferably, step S2 is specifically as follows: S21. Use the fixed bed heater 6 to receive the first cooling medium that absorbs the heat released by the catalytic conversion reaction in the fluidized bed cooler 5, and use the heated first cooling medium as the heating medium. Therefore, the high-temperature steam flowing out from the outlet of the fluidized bed cooler 5 continues to flow into the fixed bed heater 6 in the heating section 3 of the fixed bed reactor, releasing latent heat to maintain the stability of the reaction temperature in the fixed bed reactor, thereby realizing the heat recovery and cascade utilization within the system and improving the overall energy efficiency.

[0060] S3. Use the cooling section 2 of the fixed bed reactor to receive the product gas and the remaining part of the synthesis gas, and introduce the second cooling medium into the fixed bed cooler 7 in the cooling section 2, controlling the temperature of the synthesis gas entering the fixed bed reactor at 320°C - 340°C during the early stage of the reaction; S4. Use the heating section 3 of the fixed bed reactor to receive the product gas and the unreacted synthesis gas transmitted from the cooling section 2, and introduce the heating medium into the fixed bed heater 6 in the heating section 3, controlling the temperature of the synthesis gas entering the fixed bed reactor at 280°C - 300°C during the later stage of the reaction; S5. Use the cooling section 2 and the heating section 3 to enable at least the second part of the synthesis gas to be continuously catalytically converted into product gas by the fixed bed catalyst at different temperatures, realizing the deep conversion of the synthesis gas.

[0061] The product gas generated in step S2 and the unreacted syngas flow out of the outlet of the fluidized bed reactor 1 and flow to the inlet of the cooling section 2 of the fixed bed reactor for further reaction. At the same time, cooling water is introduced into the inlet of the fixed bed cooler 7 in the cooling section 2, and the reaction temperature is controlled at 320°C - 340°C. The heat-exchanged medium flows out of the outlet of the fixed bed cooler 7. Most of the product gas flowing out of the cooling section 2 and a small amount of unreacted syngas reach the heating section 3 of the fixed bed through the partition plate 4. At the same time, high-temperature steam is introduced into the inlet of the fixed bed heater 6 in the heating section 3, and the reaction continues at 280°C - 300°C. The heat-exchanged heating medium flows out of the outlet of the fixed bed heater 6.

[0062] The total single-pass conversion rate of CO reaching the outlet of the fixed bed reactor reaches 95% - 98%.

[0063] For the above method embodiments, since they are basically similar to the system embodiments, the description is relatively simple. For related parts, reference can be made to the description of the system embodiments.

[0064] To make those skilled in the art understand the present invention more clearly, a system and method for preparing olefins from syngas of the present invention will be described in detail through the following embodiments.

[0065] Example 1: A fluidized bed catalyst is loaded into the fluidized bed reactor 1. The active component of the fluidized bed catalyst is iron carbide, the promoter is sodium carbonate, the mass ratio of the promoter to the active component is 1:2, the catalyst is loaded in porous carbon, and the mass ratio of the porous carbon is 20%.

[0066] A fixed bed reactor catalyst is loaded into the fixed bed reactor. The active component of the fixed bed catalyst is iron phosphate, the promoters are 30% potassium carbonate, 30% sodium nitrate and 40% magnesium chloride, the mass ratio of the promoters to the active component is 1:30, and the catalyst is loaded in a composite support of carbon nanotubes and alumina. The mass ratio of the support is 30%.

[0067] Syngas is introduced into the fluidized bed reactor 1 and reduced at 400°C and 2 MPa for 6 h. The partial pressure of the syngas is controlled at 10%, and the rest is nitrogen. The reducing gas flows out of the gas outlet at the top of the fluidized bed reactor 1 and flows into the gas inlet at the top of the fixed bed reactor. Under the same conditions, reduction is carried out in the fixed bed reactor. The reducing gas flows out of the gas outlet at the bottom of the fixed bed reactor.

[0068] After the reduction is completed, cooling water is introduced into the fluidized bed cooler 5 of the fluidized bed reactor 1, and low-temperature syngas with a temperature of 30°C and an H2 / CO volume ratio of 1.2:1 is introduced into the gas inlet at the bottom of the fluidized bed reactor 1 to cool the catalyst, control the temperature at 370°C, and maintain the mass space velocity of the reaction at 10 h-1 , the pressure is 6 MPa.

[0069] The cooling water in the fluidized bed cooler 5 in the fluidized bed reactor 1 is heated and vaporized into high-temperature steam, which flows from the outlet of the fluidized bed cooler 5 to the inlet of the fixed bed heater 6 in the heating section 3 of the fixed bed reactor. After the primary reaction in the fluidized bed reactor 1, the single-pass conversion rate of CO reaches 75%, and the olefin selectivity accounts for 70% among hydrocarbons above C2.

[0070] The generated gas product and the unreacted syngas flow out of the fluidized bed reactor 1 through the gas outlet and then enter the cooling section 2 of the fixed bed reactor to continue the reaction. Cooling water is introduced into the inlet of the fixed bed cooler 7 in the cooling section 2 to control the reaction temperature at 338 °C, and the heat-exchanged medium flows out of the outlet of the fixed bed cooler 7.

[0071] The gas in the cooling section 2 reaches the heating section 3 of the fixed bed reactor through the partition plate 4 and continues to react at 300 °C. The high-temperature steam used to heat the heating section 3 flows out of the outlet of the fixed bed heater 6 after passing through the fixed bed heater 6.

[0072] The total single-pass conversion rate of CO at the gas outlet at the bottom of the fixed bed reactor reaches 95%.

[0073] Example 2 The fluidized bed catalyst is loaded into the fluidized bed reactor 1. The active components of the fluidized bed catalyst are iron carbide and iron borate (accounting for 90% and 10% respectively). The promoters are potassium carbonate and calcium chloride (accounting for 70% and 30% respectively). The mass ratio of the promoter to the active component is 1:5, and the catalyst is loaded on porous carbon. The mass ratio of the porous carbon is 20%.

[0074] The fixed bed reactor catalyst is loaded into the fixed bed reactor. The active components of the fixed bed catalyst are cobalt carbide and nickel carbide (accounting for 95% and 5% respectively), and the promoters are potassium chloride and sodium carbonate (accounting for 25% and 98% respectively). The mass ratio of the promoter to the active component is 1:2. The catalyst is loaded on carriers of carbon nanotubes, graphene and thorium oxide (accounting for 50%, 2% and 48% respectively). The mass ratio of the carrier is 30%.

[0075] Syngas is introduced into the fluidized bed reactor 1 and reduced at 420 °C and 2.4 MPa for 1 h. The partial pressure of the syngas is controlled at 80%, and the rest is CO2 and CH4 (each accounting for 10%). The reducing gas flows out from the gas outlet at the top of the fluidized bed reactor 1 and flows into the gas inlet at the top of the fixed bed reactor, where it is reduced in the fixed bed reactor under the same conditions. The reducing gas flows out from the gas outlet at the bottom of the fixed bed reactor.

[0076] After the reduction is completed, cooling water is introduced into the fluidized bed cooler 5 of the fluidized bed reactor 1, and low-temperature syngas with a temperature of 50 °C is introduced through the gas inlet at the bottom of the fluidized bed reactor 1. The H2 / CO volume ratio of this syngas is 2:1, so as to cool down the catalyst, control the temperature at 350 °C, and maintain the mass space velocity of the reaction at 2 h -1 , and the pressure is 5 MPa.

[0077] The cooling water in the fluidized bed cooler 5 in the fluidized bed reactor 1 is heated and vaporized into steam, and flows from the outlet of the fluidized bed cooler 5 to the inlet of the fixed bed heater 6 in the heating section 3 of the fixed bed reactor. After the primary reaction in the fluidized bed reactor 1, the single-pass conversion rate of CO reaches 90%, and the olefin selectivity accounts for 85% among hydrocarbons above C2.

[0078] The generated gas product and the unreacted syngas flow out of the fluidized bed reactor 1 through the gas outlet and then enter the cooling section 2 of the fixed bed reactor to continue the reaction. Cooling water is introduced into the inlet of the fixed bed cooler 7 in the cooling section 2, and the reaction temperature is controlled at 330 °C. The heat-exchanged medium flows out from the outlet of the fixed bed cooler 7.

[0079] The gas in the cooling section 2 passes through the partition 4 and reaches the heating section 3 of the fixed bed reactor to continue the reaction at 290 °C. The high-temperature steam used to heat the heating section 3 flows out from the outlet of the fixed bed heater 6 after passing through the fixed bed heater 6.

[0080] The total single-pass conversion rate of CO reaching the gas outlet at the bottom of the fixed bed reactor reaches 98%.

[0081] Example 3 A fluidized bed catalyst is loaded into the fluidized bed reactor 1. The active components of the fluidized bed catalyst are iron carbide and iron phosphate (accounting for 30% and 70% respectively), and the promoters are sodium nitrate and magnesium carbonate (each accounting for 50%). The mass ratio of the promoter to the active component is 1:30, and the catalyst is supported on porous carbon. The mass fraction of the porous carbon is 30%.

[0082] A fixed bed reactor catalyst is loaded into the fixed bed reactor. The active component of the fixed bed catalyst is iron carbide, and the promoters are potassium carbonate, sodium carbonate, and magnesium chloride (accounting for 35%, 60%, and 5% respectively). The mass ratio of the promoter to the active component is 1:20. The catalyst is supported on a composite support of carbon nanotubes, graphene, alumina, and silica (each accounting for 25%). The mass fraction of the support is 50%.

[0083] Hydrogen is introduced into the fluidized bed reactor 1 and reduced at 410 °C and 3 MPa for 3 h. The partial pressure of hydrogen is controlled at 50%, and the remaining is 50% CO2. The reducing gas flows out from the gas outlet at the top of the fluidized bed reactor 1 and flows into the gas inlet at the top of the fixed bed reactor. Under the same conditions, reduction is carried out in the fixed bed reactor. The reducing gas flows out from the gas outlet at the bottom of the fixed bed reactor.

[0084] After the reduction is completed, cooling water is introduced into the fluidized bed cooler 5 of the fluidized bed reactor 1, and low-temperature syngas at 20 °C is introduced from the gas inlet at the bottom of the fluidized bed reactor 1. The H2 / CO volume ratio of this syngas is 1.5:1 to cool down the catalyst, control the temperature at 360 °C, and maintain the mass space velocity of the reaction at 10 h -1 , and the pressure is 2 MPa.

[0085] The cooling water in the fluidized bed cooler 5 in the fluidized bed reactor 1 is heated and vaporized into steam, which flows from the outlet of the fluidized bed cooler 5 to the inlet of the fixed bed heater 6 in the heating section 3 of the fixed bed reactor. After the primary reaction in the fluidized bed reactor 1, the single-pass conversion rate of CO reaches 87%, and the olefin selectivity accounts for 78% among hydrocarbons with C2 and above.

[0086] The generated gas product and the unreacted syngas flow out of the fluidized bed reactor 1 through the gas outlet and enter the cooling section 2 of the fixed bed reactor to continue the reaction. Cooling water is introduced into the inlet of the fixed bed cooler 7 in the cooling section 2, and the reaction temperature is controlled at 340 °C. The heat-exchanged medium flows out from the outlet of the fixed bed cooler 7.

[0087] The gas in the cooling section 2 passes through the baffle 4 and reaches the heating section 3 of the fixed bed reactor to continue the reaction at 300 °C. The high-temperature steam for heating the heating section 3 flows out from the outlet of the fixed bed heater 6 after passing through the fixed bed heater 6.

[0088] The total single-pass conversion rate of CO reaching the gas outlet at the bottom of the fixed bed reactor reaches 97%.

[0089] Example 4 A fluidized bed catalyst is loaded into the fluidized bed reactor 1. The active components of the fluidized bed catalyst are cobalt carbide and iron phosphate (accounting for 10% and 90% respectively), and the promoters are sodium carbonate and magnesium carbonate (accounting for 10% and 90% respectively). The mass ratio of the promoter to the active component is 1:4, and the catalyst is supported on porous carbon. The mass ratio of the porous carbon is 40%.

[0090] Charge the fixed-bed reactor with the fixed-bed reactor catalyst. The active component of the fixed-bed catalyst is iron hypophosphite, and the promoters are potassium carbonate and magnesium chloride (accounting for 55% and 45% respectively). The mass ratio of the promoter to the active component is 1:10. The catalyst is loaded in a composite support of carbon nanotubes, graphene, alumina and silica (each accounting for 25%). The mass ratio of the support is 50%.

[0091] Introduce hydrogen into the fluidized-bed reactor 1 and reduce it at 415 °C and 2.5 MPa for 5 h. The partial pressure of the syngas is controlled at 60%, and the rest is 40% CO2. The reducing gas flows out from the gas outlet at the top of the fluidized-bed reactor 1 and flows into the gas inlet at the top of the fixed-bed reactor. Under the same conditions, reduction is carried out in the fixed-bed reactor. The reducing gas flows out from the gas outlet at the bottom of the fixed-bed reactor.

[0092] After the reduction is completed, cool water is introduced into the fluidized-bed cooler 5 of the fluidized-bed reactor 1, and low-temperature syngas at 40 °C is introduced from the gas inlet at the bottom of the fluidized-bed reactor 1. The H2 / CO volume ratio of the syngas is 1.8:1 to cool the catalyst, control the temperature at 360 °C, and maintain the mass space velocity of the reaction at 5 h -1 , and the pressure is 3.5 MPa.

[0093] The cool water in the fluidized-bed cooler 5 in the fluidized-bed reactor 1 is heated and vaporized into steam, and flows from the outlet of the fluidized-bed cooler 5 to the inlet of the fixed-bed heater 6 in the heating section 3 of the fixed-bed reactor. After the primary reaction in the fluidized-bed reactor 1, the single-pass conversion rate of CO reaches 83%, and the olefin selectivity accounts for 82% among hydrocarbons with C2 and above.

[0094] The generated gas product and the unreacted syngas flow out of the fluidized-bed reactor 1 through the gas outlet and enter the cooling section 2 of the fixed-bed reactor for further reaction. Cool water is introduced into the inlet of the fixed-bed cooler 7 in the cooling section 2, and the reaction temperature is controlled at 320 °C. The heat-exchanged medium flows out from the outlet of the fixed-bed cooler 7.

[0095] The gas in the cooling section 2 passes through the partition plate 4 and reaches the heating section 3 of the fixed-bed reactor for further reaction at 280 °C. The high-temperature steam for heating the heating section 3 flows out from the outlet of the fixed-bed heater 6 after passing through the fixed-bed heater 6.

[0096] The total single-pass conversion rate of CO reaching the gas outlet at the bottom of the fixed-bed reactor reaches 96.7%.

[0097] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification. For method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should be aware that the present invention is not limited by the described order of actions, because according to the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0098] The above has introduced in detail a syngas direct preparation olefin system and method with step-by-step conversion coupling and segmented temperature control provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A syngas direct preparation olefin system with step-by-step conversion coupling and segmented temperature control, characterized in that the system Comprising: A fluidized bed reactor filled with a fluidized bed catalyst and syngas inside, for catalytically converting at least a first portion of the syngas into product gas; A fixed bed reactor communicating with the fluidized bed reactor, for receiving the product gas and the remaining portion of the syngas; The fixed bed reactor is filled with a fixed bed catalyst inside, for catalytically converting at least a second portion of the syngas into product gas to achieve deep conversion of the syngas; Wherein, the fixed bed reactor includes a cooling section and a heating section that communicate with each other, and the cooling section communicates with the fluidized bed reactor. The cooling section is used to reduce the reaction temperature of the syngas in the fixed bed reactor in the early stage of the reaction, and the heating section is used to increase the reaction temperature of the syngas in the fixed bed reactor in the later stage of the reaction.

2. The syngas direct preparation olefin system with step-by-step conversion coupling and segmented temperature control according to claim 1, wherein The system further includes a partition board provided with a plurality of air holes; the partition board is arranged inside the fixed bed reactor to divide the fixed bed reactor into the cooling section and the heating section that are connected through the air holes.

3. The syngas direct preparation olefin system with step-by-step conversion coupling and segmented temperature control according to claim 2, wherein The partition board is radially arranged inside the fixed bed reactor so that the cooling section is located above the heating section.

4. The syngas direct preparation olefin system with step-by-step conversion coupling and segmented temperature control according to claim 1, characterized in that, The system further includes: A fluidized bed cooler arranged inside the fluidized bed reactor and filled with a first cooling medium inside; A fixed bed cooler arranged inside the cooling section and filled with a second cooling medium inside; A fixed bed heater arranged inside the heating section.

5. The syngas direct preparation olefin system with step-by-step conversion coupling and segmented temperature control according to claim 4, characterized in that, The fixed bed heater is filled with a heating medium; wherein, the fluidized cooler communicates with the fixed bed heater so that after the first cooling medium absorbs the heat released during the conversion of the syngas in the fluidized bed reactor, it serves as the heating medium in the fixed bed heater.

6. A syngas direct preparation olefin system with step-by-step conversion coupling and segmented temperature control according to any one of claims 1-5, characterized in that, The content of the first portion of the syngas is 75%-95% of the total content of the syngas; the content of the second portion of the syngas is 5%-25% of the total content of the syngas.

7. A method for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control, characterized in that, The method includes: Introducing syngas or hydrogen into the fluidized bed reactor and the fixed bed reactor to perform a reduction treatment on the fluidized bed catalyst loaded in the fluidized bed reactor and the fixed bed catalyst loaded in the fixed bed reactor; After the catalytic reduction ends, introducing syngas into the fluidized bed reactor, and introducing a first cooling medium into the fluidized bed cooler inside the fluidized bed reactor, controlling the temperature inside the fluidized bed reactor to be 320°C - 370°C, so that at least a first portion of the syngas is catalytically converted into product gas by the fluidized bed catalyst; Using the cooling section of the fixed bed reactor to receive the product gas and the remaining portion of the syngas, introducing a second cooling medium into the fixed bed cooler inside the cooling section, controlling the temperature of the syngas entering the fixed bed reactor in the early stage of the reaction to be 320°C - 340°C; Using the heating section of the fixed bed reactor to receive the product gas and the unconverted syngas transmitted by the cooling section, and introducing a heating medium into the fixed bed heater inside the heating section, controlling the temperature of the syngas entering the fixed bed reactor in the later stage of the reaction to be 280°C - 300°C; The at least second part of the syngas is continuously catalytically converted into product gas by the fixed-bed catalyst during different temperatures by using the cooling section and the heating section, so as to realize the deep conversion of the syngas.

8. A method for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control according to claim 7, characterized in that, Feeding a heating medium into the fixed-bed heater in the heating section includes: Using the fixed-bed heater to receive the first cooling medium that absorbs the heat released by the catalytic conversion reaction in the fluidized-bed cooler, and taking the heated first cooling medium as the heating medium.

9. The method for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control according to claim 7, characterized in that, Both the fluidized-bed catalyst and the fixed-bed catalyst include an active component and a promoter; wherein, the active component includes one or more of metal carbides, metal phosphates, and metal borates; the promoter includes one or more of carbonates, chlorides, and nitrates of potassium, sodium, calcium, and magnesium.

10. The method for directly preparing olefins from syngas with stepwise conversion coupling and segmented temperature control according to claim 9, characterized in that, The fluidized-bed catalyst further includes porous carbon, and the active component and the promoter are supported on the porous carbon; or The fixed-bed catalyst further includes a carrier, and the carrier includes one or more of carbon nanotubes, graphene, alumina, silica, and thorium oxide; the active component and the promoter are supported on the carrier.

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