Segmented heat exchange energy-saving method and system used in organic liquid dehydrogenation system

Abstract

The invention provides a sectional heat exchange energy-saving method and a sectional heat exchange energy-saving system used in an organic liquid dehydrogenation system. According to the method, based on temperature-cumulative heat exchange (TQ) curve analysis, in order to solve the problems that heat needed by dehydrogenation raw materials in a gasification phase change interval is concentrated and the heat release capacity of hydrogen-containing dehydrogenation products in the temperature zone is insufficient, an external heat source is inserted in the dehydrogenation raw material preheating process for heat compensation so as to make up a local heat matching gap; meanwhile, the high-temperature section heat of the dehydrogenation product is used for heating the high-temperature section of the dehydrogenation raw material, the medium-low-temperature section heat is used for heating the low-temperature section of the dehydrogenation raw material, and gradient efficient utilization of waste heat is achieved. And dehydrogenation products enter an external cooling unit after all heat exchange is completed. Compared with a traditional single-section heat exchange design, the heat supply temperature of an external heat source can be reduced from 360 DEG C or above to 300 DEG C or below, dependence on a high-grade heat source is remarkably reduced, and the energy-saving performance and operation flexibility of the system are improved.

Description

Technical Field

[0001] This application relates to the field of energy-saving technology in chemical processes, and more specifically, to a segmented heat exchange energy-saving method and system used in an organic liquid dehydrogenation system. Background Technology

[0002] In organic liquid hydrogen storage systems, the dehydrogenation process typically includes steps such as feedstock preheating, reaction, and product cooling. A common energy-saving design utilizes the heat released from the cooling of the dehydrogenation products to preheat the liquid dehydrogenation feedstock, thereby achieving energy recovery.

[0003] However, because the dehydrogenation products contain a large amount of hydrogen (usually exceeding 40% by volume), their heat capacity is significantly lower than that of the liquid dehydrogenation feedstock (methylcyclohexane or a mixture of it and toluene). Meanwhile, the liquid dehydrogenation feedstock undergoes a significant bubble point vaporization process during preheating, requiring a large amount of latent heat and sensible heat near the bubble point.

[0004] In temperature-to-cumulative heat exchange (TQ) curve analysis, the characteristic of "cold streams absorbing heat in a concentrated manner and hot streams releasing heat in a dispersed manner" leads to local temperature overlaps or non-overlapping areas between the two in the vaporization temperature range of the liquid dehydrogenation feedstock. Even if the total heat release of the dehydrogenation products is greater than the total heat required by the liquid dehydrogenation feedstock, it is impossible to achieve a match through a single heat exchanger. Therefore, in traditional single-stage heat exchange designs, the feedstock can only be heated to a medium temperature, still requiring a high-temperature external heat source above 360°C to heat it to the reaction temperature. This results in a strong dependence of the system on high-grade heat sources and high operating costs. To solve this problem, a segmented heat exchange method based on thermodynamic matching optimization is urgently needed to reduce the temperature requirement of the external heat source. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a segmented heat exchange energy-saving method and system for organic liquid dehydrogenation systems. Based on TQ curve analysis, it was found that within the phase change temperature range of the liquid dehydrogenation feedstock vaporization, the heat released by the dehydrogenation products due to their hydrogen content is insufficient to meet the concentrated heat absorption requirements of the feedstock, creating a localized heat matching gap. Therefore, this invention inserts an external heat source for supplemental heating within this temperature range and achieves efficient, tiered utilization of the waste heat from the dehydrogenation products by rationally allocating the heat exchange sequence.

[0006] In a first aspect, the present invention provides a segmented heat exchange energy-saving method for use in an organic liquid dehydrogenation system, comprising: S1. The dehydrogenation raw material is preheated using the heat from the medium and low temperature range of the dehydrogenation product, so that the temperature of the dehydrogenation raw material is close to or reaches the temperature of the gasification phase change. S2. During the temperature range in which the dehydrogenation feedstock undergoes gasification phase change, an external heat source is inserted for supplementary heating to make up for the heat gap between the cumulative heat absorbed by the dehydrogenation feedstock for gasification and the cumulative heat released by the dehydrogenation product in this temperature range. S3. Use the heat from the high-temperature section of the dehydrogenation product to finally raise the temperature of the dehydrogenation raw material that has been reheated, so that it approaches or reaches the dehydrogenation reaction temperature.

[0007] Optionally, the method further includes: S4. After completing the entire heat exchange process, the dehydrogenation products are then cooled in the refrigeration system.

[0008] Optionally, the heat supplied by the external heat source accounts for 15%-40% of the total heat required for preheating the dehydrogenation feedstock; The external heat source shall not exceed 300°C in temperature.

[0009] Optionally, the external heat source may be supplied with heat via electric heating or heat exchange heating. The heat exchange heating medium includes steam, heat transfer oil, or molten salt.

[0010] Optionally, the final heating raises the temperature of the dehydrogenation feedstock to not less than 280°C; The temperature difference between the dehydrogenation reaction temperature and the temperature of the dehydrogenation feedstock after final heating is less than 20°C.

[0011] Optionally, the dehydrogenation product is a mixture of methylcyclohexane after dehydrogenation reaction, comprising hydrogen, toluene and unreacted methylcyclohexane; The dehydrogenation feedstock is methylcyclohexane, or a mixture of methylcyclohexane and toluene.

[0012] In a second aspect, the present invention provides a segmented heat exchange system for use in an organic liquid dehydrogenation system, the segmented heat exchange system being used to implement the segmented heat exchange energy-saving method for the organic liquid dehydrogenation system described in the first aspect, the segmented heat exchange system comprising: First heat exchange unit (1), external heating unit (3), and second heat exchange unit (2); The cold flow inlet of the first heat exchange unit (1) is connected to the feeding unit, and the cold flow outlet of the first heat exchange unit (1) is connected to the cold flow inlet of the external heating unit (3). The cold flow outlet of the external heating unit (3) is connected to the cold flow inlet of the second heat exchange unit (2); The heat outlet of the second heat exchange unit (2) is connected to the heat inlet of the first heat exchange unit (1); The first heat exchange unit (1) is used to transfer the heat of the medium and low temperature range of the dehydrogenation product to the dehydrogenation raw material, so that it can complete the initial preheating, so that the temperature of the dehydrogenation raw material is close to or reaches the temperature of the gasification phase change. The external heating unit (3) is used to supplement the heat within the temperature range of the gasification phase change of the dehydrogenation feedstock; The second heat exchange unit (2) is used to transfer the high-temperature heat of the dehydrogenation product to the dehydrogenation raw material that has been reheated, so that it can complete the final temperature rise.

[0013] Optionally, the system further includes an external cooling unit (5); The heat inlet of the external cooling unit (5) is connected to the heat outlet of the first heat exchange unit (1); The external cooling unit (5) is used to cool the dehydrogenation product after all heat exchange has been completed.

[0014] Optionally, the temperature of the dehydrogenation product before entering the external cooling unit (5) is not lower than 80°C.

[0015] Optionally, the external heating unit (3) is an electric heater, a thermal oil heat exchanger, or a steam heater; The heating temperature of the external heating unit (3) is not higher than 300°C.

[0016] Optionally, the first heat exchange unit (1) and the second heat exchange unit (2) are each composed of one or more heat exchangers connected in series or in parallel.

[0017] Optionally, the system further includes a separation unit (6); The outlet of the external cooling unit (5) is connected to the inlet of the separation unit (6); The separation unit (6) is used to separate hydrogen from the dehydrogenation products cooled to 25°C-30°C.

[0018] Optionally, the system further includes a dehydrogenation reaction unit (4). The product outlet of the dehydrogenation reaction unit (4) is connected to the heat inlet of the second heat exchange unit (2).

[0019] In summary, the present invention has at least one of the following beneficial technical effects: This invention provides a segmented heat exchange energy-saving method and system for use in organic liquid dehydrogenation systems. By using the heat from the high-temperature section of the dehydrogenation product to heat the high-temperature section of the liquid dehydrogenation feedstock, and using the heat from the medium- and low-temperature section of the dehydrogenation product to heat the low-temperature section of the liquid dehydrogenation feedstock, the energy level mismatch problem of "high-temperature heat source used for low-temperature heating" or "low-temperature waste heat used for high-temperature heating" in traditional single-stage heat exchange is avoided, thereby improving the overall thermal efficiency of the system.

[0020] In this invention, the dehydrogenation products enter the external heat exchanger only after completing the entire heat exchange process (including the high-temperature section and the medium-low temperature section), avoiding heat waste caused by premature cooling and significantly reducing the load on the cooling utility.

[0021] The system provided by this invention has clearly defined functions for each heat exchange unit and a fixed connection sequence, which facilitates engineering implementation and operation control. At the same time, it allows for flexible selection of external heat source forms (such as electric heating, steam, or heat transfer oil) according to the raw material flow rate, composition, or reaction temperature requirements, adapting to various working conditions. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The temperature-cumulative heat transfer curves for the cooling of dehydrogenation products and the preheating of dehydrogenation feedstock in the relevant technology are shown. Figure 2 The temperature-cumulative heat exchange curve of a single-stage, one-time heat exchange process for dehydrogenation products and dehydrogenation feedstock in the relevant technology is shown. Figure 3 The temperature-cumulative heat exchange curves of the segmented heat exchange process between dehydrogenation product and dehydrogenation feedstock proposed in this embodiment of the invention are shown. Figure 4 A flowchart of the segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system proposed in this embodiment of the invention is shown. Figure 5 A schematic diagram of the segmented heat exchange energy-saving system used in the organic liquid dehydrogenation system proposed in an embodiment of the present invention is shown. Figure 6 A schematic diagram of the single-stage primary heat exchange system for the organic liquid dehydrogenation process proposed in Comparative Example 1 of this invention is shown.

[0024] Explanation of reference numerals in the attached figures: 1. First heat exchange unit; 11. First piping; 2. Second heat exchange unit; 21. Fourth piping; 3. External heating unit; 31. Second pipe; 4. Dehydrogenation reaction unit; 41. Third pipeline; 5. External cooling unit; 6. Separation unit; 7. Transfer pump; 71. Fifth pipeline; 8. Dehydrogenation reactor; 9. First heat exchanger; 10. Second heat exchanger; 101. Third heat exchanger. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] In the accompanying drawings, the size of constituent elements, the thickness of layers, or areas may sometimes be exaggerated for clarity. Therefore, any implementation of this disclosure is not necessarily limited to the dimensions shown in the drawings, and the shapes and sizes of the components in the drawings do not reflect true proportions. Furthermore, the drawings schematically illustrate ideal examples, and any implementation of this disclosure is not limited to the shapes or values ​​shown in the drawings.

[0027] In related technologies, methylcyclohexane is a typical hydrogen storage carrier in organic liquid hydrogen storage systems. Its dehydrogenation process typically includes steps such as feedstock feeding, preheating, reaction, product cooling, and separation. A common energy-saving design utilizes the heat released from the cooling of the dehydrogenation products to preheat the liquid organic hydrogen storage feedstock, thereby achieving energy recovery.

[0028] However, because the dehydrogenation products contain a large amount of hydrogen (usually exceeding 40% by volume), their specific heat capacity is significantly lower than that of the liquid dehydrogenation feedstock (methylcyclohexane or a mixture of it and toluene). Meanwhile, the liquid dehydrogenation feedstock undergoes a significant bubble point vaporization process during preheating, and its endothermic effect is concentrated near the bubble point, including both latent and sensible heat.

[0029] Figure 1 The temperature-cumulative heat transfer curves for the cooling of dehydrogenation products and the preheating of dehydrogenation feedstock in the relevant technology are shown. Figure 2 The temperature-cumulative heat exchange curves of a single-stage, one-time heat exchange process for dehydrogenation products and feedstock in related technologies are shown. Figure 1 and Figure 2 As shown in the temperature-cumulative heat exchange (TQ) curve analysis, this characteristic of "cold streams absorbing heat in a concentrated manner and hot streams releasing heat in a dispersed manner" leads to local temperature overlaps or non-overlapping areas between the two in the feedstock gasification temperature range. Even if the total heat release of the dehydrogenation products is greater than the total heat required by the liquid organic hydrogen storage feedstock (i.e., the dehydrogenation feedstock), it cannot be matched by a single heat exchanger. Therefore, in the traditional single-stage single-heat exchange design, the dehydrogenation feedstock can only be heated to a medium temperature (e.g., 243℃), still requiring a high-temperature external heat source above 360℃ to heat it to the reaction temperature (300℃-400℃), resulting in a strong dependence of the system on high-grade heat sources and high operating costs.

[0030] To address this problem, this invention proposes a segmented heat exchange energy-saving method based on thermodynamic matching optimization. Figure 3The temperature-cumulative heat transfer curves of the segmented heat exchange process between dehydrogenation product and dehydrogenation feedstock proposed in this embodiment of the invention are shown, as follows: Figure 3 As shown, in the vaporization phase change temperature range of liquid organic hydrogen storage feedstock (i.e., dehydrogenation feedstock) (approximately 120℃-160℃), the heat release from the dehydrogenation products due to their hydrogen content is insufficient to meet the concentrated heat absorption requirements of the dehydrogenation feedstock, resulting in a localized heat matching gap. To address this, this embodiment of the invention inserts an external heat source for medium-temperature supplementary heating within this temperature range. By rationally arranging the heat exchange sequence, the heat from the high-temperature section of the dehydrogenation products is used to heat the high-temperature section of the liquid dehydrogenation feedstock, and the heat from the medium- and low-temperature sections is used to heat the low-temperature section of the liquid dehydrogenation feedstock, achieving efficient cascade utilization of waste heat. The dehydrogenation products only enter the external cooling unit after completing the entire heat exchange process, maximizing waste heat recovery.

[0031] Figure 4 A flowchart of the segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system proposed in this embodiment of the invention is shown, as follows: Figure 4 As shown, it specifically includes: Step S1: Use the heat from the medium and low temperature range of the dehydrogenation product to preheat the dehydrogenation feedstock so that the temperature of the dehydrogenation feedstock is close to or reaches the temperature of the gasification phase change. It should be noted that in step S1, during the heat exchange in the medium and low temperature section (preliminary preheating of the dehydrogenation feedstock), the above-mentioned medium and low temperature dehydrogenation product is exchanged with the low temperature dehydrogenation feedstock (temperature not higher than 50°C). After the preliminary preheating is completed, the temperature of the dehydrogenation feedstock is not lower than 100°C. Preferably, the dehydrogenation feedstock is preheated to 100°C-160°C, and the temperature is close to or reaches the bubble point temperature of the dehydrogenation feedstock. The medium and low temperature dehydrogenation product is cooled to not higher than 100°C. In some embodiments, the dehydrogenation product is a mixture of methylcyclohexane after dehydrogenation reaction, comprising hydrogen, toluene and unreacted methylcyclohexane; The dehydrogenation feedstock is methylcyclohexane, or a mixture of methylcyclohexane and toluene.

[0032] This invention addresses the characteristics of high hydrogen content and extremely low heat capacity in the dehydrogenation products of methylcyclohexane, or a mixture of methylcyclohexane and toluene. By setting up segmented heat exchange, it effectively overcomes the limitations of traditional single-stage heat exchange. The external heat source only needs to provide medium-temperature supplementary heat (heating temperature below 300°C), avoiding the use of high-temperature heat sources above 360°C in traditional processes.

[0033] Step S2: In the temperature range during which the dehydrogenation feedstock undergoes gasification phase change, an external heat source is inserted for supplementary heating to make up for the heat gap between the cumulative heat absorbed by the dehydrogenation feedstock for gasification and the cumulative heat released by the dehydrogenation product in this temperature range. It should be noted that in step S2, during the intermediate-temperature supplementary heating (to make up for the heat matching gap), after the dehydrogenation feedstock has completed its initial preheating and before entering the high-temperature heat exchange section, an external heat source is used to heat it to raise its temperature to 150℃-260℃; preferably, the temperature of the dehydrogenation feedstock is raised to 250℃-260℃ to make up for the heat matching gap caused by insufficient heat release of the hot flow in the gasification phase change zone of the dehydrogenation feedstock. It should also be noted that, in some embodiments, the heat supplemented by the external heat source accounts for 15%-40% of the total heat required for preheating the dehydrogenation feedstock; The external heat source shall not exceed 300°C in temperature.

[0034] For example, the heat supplemented by the external heat source accounts for 15%, 20%, 25%, 30%, 35%, and 40% of the total heat required for preheating the dehydrogenation feedstock. In the segmented heat exchange process of this embodiment of the invention, by controlling the heat supplemented by the external heat source, the dependence on the high-temperature external heat source is reduced, thereby achieving the production goal of energy saving and emission reduction. In some embodiments, the external heat source provides heat via electric heating or heat exchange heating. The heat exchange heating medium includes steam, heat transfer oil, or molten salt.

[0035] It should be noted that electric heating can utilize grid power, renewable energy power, or electricity storage during off-peak hours; The embodiments of the present invention provide two optional methods: electric heating and heat exchange heating, with diversified energy supply methods, and the optimal heating scheme can be selected according to the actual working conditions.

[0036] Step S3: Use the heat from the high-temperature section of the dehydrogenation product to finally raise the temperature of the dehydrogenation raw material that has been reheated, so that it approaches or reaches the dehydrogenation reaction temperature.

[0037] In some embodiments, the final heating raises the temperature of the dehydrogenation feedstock to not less than 280°C; The temperature difference between the dehydrogenation reaction temperature and the temperature of the dehydrogenation feedstock after final heating is less than 20°C.

[0038] It should be noted that in step S3, during the high-temperature heat exchange (final heating of the dehydrogenation feedstock), the high-temperature dehydrogenation product (temperature not lower than 350°C) is exchanged with the dehydrogenation feedstock that has completed the medium-temperature reheating, so that the dehydrogenation feedstock completes the final heating to not lower than 300°C, forming a high-temperature dehydrogenation feedstock; preferably, after the final heating, the temperature of the dehydrogenation feedstock is not lower than 340°C, and the dehydrogenation product forms a medium-low temperature dehydrogenation product; In some embodiments, the method further includes: S4. After completing the entire heat exchange process, the dehydrogenation products are then cooled in the refrigeration system.

[0039] It should be noted that in step S4, during delayed cooling and separation, after the dehydrogenation product has undergone two heat exchanges in steps S1 and S3, it is cooled by a cold utility to reduce its temperature to 25°C-30°C before hydrogen separation.

[0040] It should also be noted that the cold utility is a circulating water or air cooling system; in this embodiment of the invention, the cold utility is introduced only after all heat exchange treatment of the dehydrogenation products has been completed, and the waste heat below 100°C is recovered through the refrigerant to further reduce the total energy consumption of the system.

[0041] In summary, the embodiments of this invention, through segmented heat exchange, better match the temperature change curves of the heating process of the low-temperature dehydrogenation feedstock with the cooling process of the high-temperature dehydrogenation product, especially suitable for the large differences in heat capacity of hydrogen-containing systems. Furthermore, it reduces the need for external heat sources to provide supplemental heating in the mid-temperature range, replacing the high-temperature heat source requirement of >360°C in traditional processes, fundamentally lowering the heat quality. With the reduced external heat source temperature, more readily available industrial waste heat or low-pressure steam can be used, reducing reliance on dedicated high-temperature heating equipment (such as high-temperature combustion furnaces) and lowering operational risks and control complexity.

[0042] Figure 5 A schematic diagram of the segmented heat exchange energy-saving system used in the organic liquid hydrogen storage system proposed in this embodiment of the invention is shown, as follows: Figure 5 As shown, it specifically includes: First heat exchange unit 1, external heating unit 3, and second heat exchange unit 2; The cold flow inlet of the first heat exchange unit 1 is connected to the feeding unit, and the cold flow outlet of the first heat exchange unit 1 is connected to the cold flow inlet of the external heating unit 3. The cold flow outlet of the external heating unit 3 is connected to the cold flow inlet of the second heat exchange unit 2; The heat outlet of the second heat exchange unit 2 is connected to the heat inlet of the first heat exchange unit 1; The first heat exchange unit 1 is used to transfer the heat from the medium and low temperature range of the dehydrogenation product to the dehydrogenation raw material, so as to preheat it and make the temperature of the dehydrogenation raw material approach or reach the temperature of the gasification phase change. The external heating unit 3 is used to supplement the heat within the temperature range of the gasification phase change of the dehydrogenation feedstock. The second heat exchange unit 2 is used to transfer the heat from the high-temperature section of the dehydrogenation product to the dehydrogenation raw material that has been reheated, so that it can complete the final temperature rise.

[0043] It should be noted that the first heat exchange unit 1 and the second heat exchange unit 2 can be shell and tube heat exchangers to enable efficient heat exchange between the dehydrogenation feedstock and the dehydrogenation product without contact. like Figure 5 As shown, the cold flow inlet on the first heat exchange unit 1 is connected to the feeding unit and is used to deliver low-temperature dehydrogenation raw material to the first heat exchange unit 1. The cold flow outlet is connected to the cold flow inlet of the external heating unit 3 through the first pipe 11 so as to deliver the preheated dehydrogenation raw material to the external heating unit 3. In some embodiments, such as Figure 5 As shown, the system also includes a dehydrogenation reaction unit 4; The product outlet of the dehydrogenation reaction unit 4 is connected to the heat inlet of the second heat exchange unit 2.

[0044] It should be noted that the cold flow outlet on the external heating unit 3 is connected to the cold flow inlet of the second heat exchange unit 2 via the second pipe 31, so as to transport the reheated dehydrogenation raw material to the second heat exchange unit 2. The heat inlet on the second heat exchange unit 2 is connected to the product outlet on the dehydrogenation reaction unit 4 via a third pipe 41, so that the high-temperature dehydrogenation product produced by the dehydrogenation reaction unit 4 can be directly transported to the second heat exchange unit 2 to participate in heat exchange. The heat outlet on the second heat exchange unit 2 is connected to the heat inlet of the first heat exchange unit 1 via a fourth pipe 21, so as to transport the dehydrogenation product that has completed the heat exchange in the high-temperature section to the first heat exchange unit 1, and use the heat in the low-temperature section to heat the low-temperature dehydrogenation raw material. In some embodiments, such as Figure 5 As shown, the external heating unit 3 is an electric heater, a thermal oil heat exchanger, or a steam heater; The heating temperature of the external heating unit 3 is not higher than 300°C.

[0045] It should be noted that the external heating unit 3 is connected to the thermal utility system, and the two together form an external heat source. The thermal utility system is an electrical system or a heat exchange medium supply system to provide electricity or heat exchange medium to the external heating unit 3. When the thermal utility system is a heat exchange medium supply system, the heat exchange heating medium includes steam or thermal oil. At the same time, the inlet and outlet of the thermal oil heat exchanger or steam heater are connected to the thermal utility system, so that the heat exchange medium enters the external heating unit 3 through the inlet to heat the dehydrogenation feedstock, and the cooled heat exchange medium flows back to the thermal utility system through the outlet for recycling.

[0046] In this embodiment of the invention, the combination of the first heat exchange unit 1, the external heating unit 3, and the second heat exchange unit 2 forms a closed-loop thermal circulation path. This allows the low-to-medium temperature dehydrogenation products to serve as the heat source for the first heat exchange unit 1, recovering the low-to-medium temperature waste heat from the dehydrogenation products. The external heating unit 3 is positioned between the two heat exchange cycles, requiring only medium-temperature supplementary heating of the preheated dehydrogenation feedstock to significantly reduce the external heat source's supply temperature (below 300°C). The second heat exchange unit 2 is connected to the dehydrogenation reaction unit 4, enabling immediate heat capture of the high-temperature dehydrogenation products (≥350°C) and preventing heat loss during the high-temperature phase. The system structure in this embodiment allows for independent control of each unit, improving adaptability to the flow rate / composition of the dehydrogenation feedstock, resulting in higher energy recovery efficiency and better operational flexibility.

[0047] In some embodiments, such as Figure 5 As shown, the system also includes a delivery pump 7; The inlet of the transfer pump 7 is connected to the outlet of the feeding unit (which is any storage device), and the outlet of the transfer pump 7 is connected to the cold flow inlet of the first heat exchange unit 1 via a pipeline, so as to transport the low-temperature (temperature below 30°C) dehydrogenation raw material in the feeding unit to the first heat exchange unit 1.

[0048] In some embodiments, such as Figure 5 As shown, the system also includes an external cooling unit 5; The heat inlet of the external cooling unit 5 is connected to the heat outlet of the first heat exchange unit 1; The external cooling unit 5 is used to cool the dehydrogenation product after all heat exchange has been completed.

[0049] It should be noted that, as Figure 5 As shown, the cooling unit is connected to the refrigeration utility, which is a circulating water or air cooling system; The inlet and outlet of the cooling unit are connected to the refrigeration utility to achieve water or air circulation cooling. In some embodiments, the temperature of the dehydrogenation product before entering the external cooling unit 5 is not lower than 80°C.

[0050] In some embodiments, the dehydrogenation products that have undergone complete heat exchange are cooled to below 30°C.

[0051] In this embodiment of the invention, a cooling unit is provided to cool the dehydrogenation products (≤100℃) that have completed all heat exchange to ≤30℃, so as to recover the low-temperature heat of the dehydrogenation products and improve the thermal efficiency of the system.

[0052] In some embodiments, such as Figure 5 As shown, the system also includes a separation unit 6; The outlet of the external cooling unit 5 is connected to the inlet of the separation unit 6; The separation unit 6 is used to separate hydrogen from the dehydrogenation products cooled to 25°C-30°C.

[0053] It should be noted that separation unit 6 can be a gas-liquid separator; After cooling, the dehydrogenation product is separated by separation unit 6 to obtain hydrogen, toluene, and a small amount of unreacted methylcyclohexane.

[0054] In this embodiment of the invention, the external cooling unit 5 cools the dehydrogenation products to ≤30°C, significantly improving the liquefaction degree of the mixed gas. The separation unit 6 can extract high-purity hydrogen, reducing the additional energy consumption of gas compression and purification in traditional processes. At the same time, toluene and unreacted methylcyclohexane are fully liquefied at low temperature, and the separation unit 6 can recover the liquid components, achieving near-zero raw material loss.

[0055] In some embodiments, the first heat exchange unit 1 and the second heat exchange unit 2 are each composed of one or more heat exchangers connected in series or in parallel.

[0056] It should be noted that the first heat exchange unit 1 can be composed of one or more heat exchangers connected in series or in parallel; The second heat exchange unit 2 can be composed of one or more heat exchangers connected in series or in parallel; For example, the first heat exchange unit 1 may include two, four, six, or eight heat exchangers; The second heat exchange unit 2 may include two, three, five, or seven heat exchangers; in the system provided by the embodiments of the present invention, each heat exchange process can be implemented by using one or more heat exchangers connected in parallel or in series, depending on the requirements of logistics specifications, temperature difference control, etc.

[0057] To enable those skilled in the art to more clearly understand the present invention, the segmented heat exchange energy-saving method and system used in the organic liquid dehydrogenation system of the present invention will now be described in detail through the following embodiments.

[0058] Example 1 Reference Figure 5 The structure of the segmented heat exchange energy-saving system is shown.

[0059] In this embodiment, the dehydrogenation product (hot stream) is cooled from 350°C to 25°C, and the dehydrogenation feedstock (cold stream) is heated from 25°C to 340°C. The specific process flow is as follows: (1) The dehydrogenation feedstock enters the first heat exchange unit 1, and the dehydrogenation product enters the first heat exchange unit 1 at the same time. The heat of the medium and low temperature section of the dehydrogenation product is used to preheat the dehydrogenation feedstock, so that the dehydrogenation feedstock is heated from 25°C to 147°C (this temperature is close to or reaches the temperature of gasification phase change), and the temperature of the dehydrogenation product is reduced from 274°C to 82°C. (2) After initial preheating, the dehydrogenated feedstock then enters the external heating unit 3. The electric heater completes the supplementary heating in the temperature range where the dehydrogenated feedstock undergoes gasification phase change, so as to make up for the heat gap between the cumulative heat absorbed by the dehydrogenated feedstock for gasification and the cumulative heat released by the dehydrogenated products in the temperature range, so that the dehydrogenated feedstock is heated from 147°C to 258°C. (3) The dehydrogenated raw material after reheating enters the second heat exchange unit 2. The high-temperature dehydrogenated product is discharged from the dehydrogenation reaction unit 4 and enters the second heat exchange unit 2. The heat of the high-temperature section of the dehydrogenated product is used to finally raise the temperature of the dehydrogenated raw material to 340°C (which is close to or reaches the dehydrogenation reaction temperature). Then it is transported to the dehydrogenation reaction unit 4 for dehydrogenation reaction. The temperature of the high-temperature dehydrogenated product decreases from 350°C to 274°C to form a medium-low temperature dehydrogenated product. The medium-low temperature dehydrogenated product is then transported to the first heat exchange unit 1 to continue to participate in subsequent heat exchange. (4) The dehydrogenation products that have completed all heat exchange treatments enter the external cooling unit 5 and are cooled to 25°C using the cold utility (circulating water). They are then transported to the separation unit 6 for hydrogen separation treatment to obtain hydrogen, toluene and a small amount of methylcyclohexane.

[0060] It should be noted that the dehydrogenation feedstock can only reach 340°C after the final heating. This is because the final preheating is provided by the dehydrogenation products, and the upper limit of the preheating temperature is limited to meet the requirement of a minimum heat transfer temperature difference of 10°C. The final reaction temperature of 350°C required by the dehydrogenation feedstock is achieved by internal heating in dehydrogenation reaction unit 4.

[0061] In the segmented heat exchange process of Example 1, the total heat required for preheating the dehydrogenation feedstock is 4388kW, the total heat released during the cooling of the dehydrogenation product is 4957kW, the heat load of the first heat exchange unit 1 is 2388kW, the heating unit provides 1071kW of heat, the heat load of the second heat exchange unit 2 is 929kW, and the heat removed by the external cooling unit 5 is 1640kW.

[0062] Comparative Example 1 Reference Figure 6 The traditional single-stage primary heat exchange system shown is illustrated.

[0063] Comparative Example 1 is a traditional single-stage heat exchange design, in which the dehydrogenation product is cooled from 350°C to 25°C, and the dehydrogenation feedstock is heated from 25°C to 340°C.

[0064] The specific process is as follows: (1) The dehydrogenation product enters the first heat exchanger 9 from the reactor outlet and its temperature drops from 350°C to 83°C after exchanging heat with the dehydrogenation feedstock; the dehydrogenation feedstock is heated from 25°C to 243°C in the first heat exchanger 9. (2) The dehydrogenated feedstock then enters the second heat exchanger 10 and is heated to 340°C by an external heat source; (3) The dehydrogenation products enter the third heat exchanger 101 from the outlet of the first heat exchanger 9 and are cooled to 25°C by circulating water.

[0065] In this process, the actual heat exchange capacity of the first heat exchanger 9 is 3296kW, the external heat source required for the second heat exchanger 10 is 1212kW, and the refrigeration load of the third heat exchanger 101 is 1661kW.

[0066] Since the raw material can only be heated to 243°C in the first heat exchanger 9, it still needs to be heated to 340°C through the second heat exchanger 10. Therefore, the heat source temperature required by the second heat exchanger 10 must be higher than 360°C to meet the heat transfer drive temperature difference requirements.

[0067] In Embodiment 1 of the present invention, under the premise of meeting the minimum heat transfer temperature difference of 10°C, the required temperature of the external heat source (external heating unit 3) is only above 157°C, which is significantly lower than that of Comparative Example 1.

[0068] In summary, this invention achieves a better thermodynamic matching between hot and cold streams through a segmented heat exchange design. Compared with traditional single-stage heat exchange, the external heat source temperature is reduced from above 360℃ to below 300℃, eliminating the need for a high-temperature external heat source to meet the heating requirements of the raw materials. This significantly improves the system's energy efficiency and operational flexibility, making it suitable for various dehydrogenation reaction conditions and demonstrating promising industrial application prospects and promotional value.

[0069] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0070] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0071] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0072] The above provides a detailed description of a segmented heat exchange energy-saving method and system for use in an organic liquid dehydrogenation system. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A segmented heat exchange energy-saving method for use in an organic liquid dehydrogenation system, characterized in that: include: S1. The dehydrogenation raw material is preheated using the heat from the medium and low temperature range of the dehydrogenation product, so that the temperature of the dehydrogenation raw material is close to or reaches the temperature of the gasification phase change. S2. During the temperature range in which the dehydrogenation feedstock undergoes gasification phase change, an external heat source is inserted for supplementary heating to make up for the heat gap between the cumulative heat absorbed by the dehydrogenation feedstock for gasification and the cumulative heat released by the dehydrogenation product in this temperature range. S3. Use the heat from the high-temperature section of the dehydrogenation product to finally raise the temperature of the dehydrogenation raw material that has been reheated, so that it approaches or reaches the dehydrogenation reaction temperature.

2. The segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system according to claim 1, characterized in that: The method further includes: S4. After completing the entire heat exchange process, the dehydrogenation products are then cooled in the refrigeration system.

3. The segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system according to claim 1, characterized in that: The heat supplied by the external heat source accounts for 15%-40% of the total heat required for preheating the dehydrogenation feedstock; The external heat source shall not exceed 300°C in temperature.

4. The segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system according to claim 1 or 3, characterized in that: The external heat source provides heat through either electric heating or heat exchange heating. The heat exchange heating medium includes steam, heat transfer oil, or molten salt.

5. The segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system according to claim 1, characterized in that: The final heating raises the temperature of the dehydrogenation feedstock to not less than 280°C; The temperature difference between the dehydrogenation reaction temperature and the temperature of the dehydrogenation feedstock after final heating is less than 20°C.

6. The segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system according to claim 1, characterized in that: The dehydrogenation product is a mixture of methylcyclohexane after dehydrogenation reaction, containing hydrogen, toluene and unreacted methylcyclohexane; The dehydrogenation feedstock is methylcyclohexane, or a mixture of methylcyclohexane and toluene.

7. A segmented heat exchange system for use in an organic liquid dehydrogenation system, characterized in that: The segmented heat exchange system is used to implement the segmented heat exchange energy-saving method in the organic liquid dehydrogenation system according to any one of claims 1-6, and the segmented heat exchange system includes: First heat exchange unit (1), external heating unit (3), and second heat exchange unit (2); The cold flow inlet of the first heat exchange unit (1) is connected to the feeding unit, and the cold flow outlet of the first heat exchange unit (1) is connected to the cold flow inlet of the external heating unit (3). The cold flow outlet of the external heating unit (3) is connected to the cold flow inlet of the second heat exchange unit (2); The heat outlet of the second heat exchange unit (2) is connected to the heat inlet of the first heat exchange unit (1); The first heat exchange unit (1) is used to transfer the heat of the medium and low temperature range of the dehydrogenation product to the dehydrogenation raw material, so that it can complete the initial preheating, so that the temperature of the dehydrogenation raw material is close to or reaches the temperature of the gasification phase change. The external heating unit (3) is used to supplement the heat within the temperature range of the gasification phase change of the dehydrogenation feedstock; The second heat exchange unit (2) is used to transfer the high-temperature heat of the dehydrogenation product to the dehydrogenation raw material that has been reheated, so that it can complete the final temperature rise.

8. The segmented heat exchange system used in the organic liquid dehydrogenation system according to claim 7, characterized in that: The system also includes an external cooling unit (5); The heat inlet of the external cooling unit (5) is connected to the heat outlet of the first heat exchange unit (1); The external cooling unit (5) is used to cool the dehydrogenation product after all heat exchange has been completed.

9. The segmented heat exchange system used in the organic liquid dehydrogenation system according to claim 8, characterized in that: The temperature of the dehydrogenation product before entering the external cooling unit (5) is not lower than 80°C.

10. The segmented heat exchange system used in the organic liquid dehydrogenation system according to claim 7, characterized in that: The external heating unit (3) is an electric heater, a heat transfer oil heat exchanger, or a steam heater; The heating temperature of the external heating unit (3) is not higher than 300°C.

11. The segmented heat exchange system used in the organic liquid dehydrogenation system according to claim 7, characterized in that: The first heat exchange unit (1) and the second heat exchange unit (2) are each composed of one or more heat exchangers connected in series or in parallel.

12. The segmented heat exchange system used in the organic liquid dehydrogenation system according to claim 8, characterized in that: The system also includes a separation unit (6); The outlet of the external cooling unit (5) is connected to the inlet of the separation unit (6); The separation unit (6) is used to separate hydrogen from the dehydrogenation products cooled to 25°C-30°C.

13. The segmented heat exchange system used in the organic liquid dehydrogenation system according to claim 7, characterized in that: The system also includes a dehydrogenation reaction unit (4); The product outlet of the dehydrogenation reaction unit (4) is connected to the heat inlet of the second heat exchange unit (2).

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