A method and system for waste heat recovery and utilization in an organic liquid dehydrogenation process

Abstract

The present application provides a waste heat recovery and utilization method and system for an organic liquid dehydrogenation process, which increases the self-supplied ratio of energy for preheating the liquid hydrogen-rich carrier from less than 75% to fully covering the energy consumption of the preheating stage, greatly improving the energy utilization rate of the process, and significantly reducing the supply of cold and hot utilities, thereby reducing operating costs. The quality of the waste heat source of the gaseous dehydrogenation product can be improved through pressurization and heat exchange, and it can be flexibly matched with the demand side, reducing the amount of heat required for the reaction and the generation of heat medium water, etc. The hydrogen finally separated has a certain adjustable range of pressure, which can meet the pressurization requirements of the back-end use scenarios, and greatly reduces the equipment footprint and investment costs of hydrogen pressurization in the back-end of conventional processes. Compared with the traditional dehydrogenation process, the overall energy efficiency of the process system is greatly improved, and the overall dehydrogenation process equipment footprint and operating energy consumption are effectively reduced.

Description

Technical Field

[0001] The present application relates to the technical field of organic liquid hydrogen storage, and in particular to a method and system for recovering waste heat from an organic liquid dehydrogenation process. Background Art

[0002] Hydrogen energy is an ideal alternative to traditional fossil fuels and is becoming an important carrier of global energy transformation. However, due to the mismatch between hydrogen supply and demand in my country, as well as the problems of low cost and difficulty in hydrogen storage and transportation, the large-scale application of hydrogen energy is severely restricted. Organic liquid hydrogen storage technology has great development potential in large-scale hydrogen storage and transportation, transoceanic transportation, and international hydrogen trade due to its advantages of large hydrogen storage capacity, high hydrogen storage density, and reversible hydrogen storage process.

[0003] The working principle of organic liquid hydrogen storage technology can be divided into two links: hydrogenation and dehydrogenation: 1) Hydrogenation: Hydrogen is added to the liquid hydrogen storage carrier through a catalytic reaction to form a liquid hydrogen-rich carrier that can be stably stored under normal temperature and pressure conditions; 2) Dehydrogenation: The liquid hydrogen-rich carrier undergoes a catalytic dehydrogenation reaction under certain temperature conditions. After the dehydrogenation product is separated into gas and liquid, the hydrogen is transported to the hydrogen-using end.

[0004] At present, the conventional thermal design for the dehydrogenation process mainly includes preheating the liquid hydrogen-rich carrier with the gaseous dehydrogenation product, and then further superheating the hydrogen-rich carrier after preheating to make it reach the temperature required for the dehydrogenation reaction. After the heat exchange, the dehydrogenation product is further cooled and separated into gas and liquid to obtain hydrogen.

[0005] However, in conventional thermal design, the dehydrogenation product contains a large amount of hydrogen. The presence of a large amount of hydrogen will cause the dew point slip of the dehydrogenation organic carrier, which will gradually condense as the temperature decreases. This special condensation process will cause the heat exchange between the liquid hydrogen-rich carrier and the dehydrogenation product to be carried out only within a small temperature range, making it impossible to utilize the large amount of waste heat generated in the dehydrogenation process, and its energy-saving effect is poor. Summary of the invention

[0006] To solve the above problems, the present application provides a method and system for recovering and utilizing waste heat from an organic liquid dehydrogenation process. The waste heat recovery method is implemented by using a newly designed system to significantly increase the heat exchange rate between the dehydrogenation product and the liquid hydrogen-rich carrier, omit the step of further superheating treatment, reduce the utility consumption of the dehydrogenation process, realize self-supply of energy during the operation of the device, improve the comprehensive energy utilization rate of the dehydrogenation process, reduce process energy consumption and operating costs, and achieve better energy-saving effects.

[0007] In a first aspect, the present application provides a method for recovering waste heat from an organic liquid dehydrogenation process, the method comprising:

[0008] S1. After compressing and pressurizing the gaseous dehydrogenation product outputted from the reaction device, the product is used for heat exchange with a liquid hydrogen-rich carrier, so that the liquid hydrogen-rich carrier is heated and vaporized to form a gaseous hydrogen-rich carrier;

[0009] S2, inputting the gaseous hydrogen-rich carrier into the reaction device for dehydrogenation treatment to obtain the gaseous dehydrogenation product;

[0010] Wherein, the difference between the dew point temperature of the gaseous dehydrogenation product after the compression and supercharging treatment and the dew point temperature of the liquid hydrogen-rich carrier is greater than the minimum heat transfer temperature difference;

[0011] The gaseous dehydrogenation product comprises a gaseous dehydrogenated organic carrier and hydrogen.

[0012] Further, in step S2, the temperature of the dehydrogenation treatment is 300°C to 480°C; and the pressure of the dehydrogenation treatment is 0.2 MPa to 0.4 MPa.

[0013] Furthermore, the pressure of the gaseous dehydrogenation product after the compression and pressurization treatment is 0.5 MPa~1.6 MPa;

[0014] The temperature of the gaseous hydrogen-rich carrier obtained by the heat exchange treatment is 350°C to 485°C;

[0015] The temperature of the gaseous dehydrogenation product after the compression and pressurization treatment is 70°C to 100°C after heat exchange treatment.

[0016] Furthermore, the compression ratio of the compression and supercharging process is 2-6.

[0017] Furthermore, the method further comprises:

[0018] The gaseous dehydrogenation product after the heat exchange treatment is collected and subjected to heat exchange cooling to liquefy the dehydrogenation organic carrier in the gaseous dehydrogenation product and separate it from the hydrogen.

[0019] Furthermore, the pressure of the separated hydrogen is 0.5 MPa~1.6 MPa.

[0020] Furthermore, the heat exchange cooling uses cooling water as the heat exchange medium.

[0021] In a second aspect, the present application provides a waste heat recovery and utilization system for an organic liquid dehydrogenation process, the system being applicable to the waste heat recovery and utilization method for the above-mentioned organic liquid dehydrogenation process, the system comprising: a hydrogen-rich liquid storage device, a heat exchange device, a reaction device and a compression device;

[0022] The liquid outlet of the hydrogen-rich liquid storage device is connected to the heat exchange device for conveying liquid hydrogen-rich carrier to the heat exchange device;

[0023] The feed port of the reaction device is connected to the heat exchange device, and is used to pass the superheated gaseous hydrogen-rich carrier into the reaction device for dehydrogenation treatment;

[0024] The discharge port of the reaction device is connected to the compression device, and is used to send the gaseous dehydrogenation product into the compression device for compression and pressurization treatment, so that the difference between the bubble dew point temperature of the gaseous dehydrogenation product and the bubble dew point temperature of the liquid hydrogen-rich carrier is greater than the minimum heat transfer temperature difference;

[0025] The compression device is connected to the heat exchange device and is used to transport the gaseous dehydrogenation product after compression and pressurization treatment to the heat exchange device for heat exchange treatment with the liquid hydrogen-rich carrier to obtain the superheated gaseous hydrogen-rich carrier.

[0026] Furthermore, the system also includes: a cooling device, a separation device, a hydrogen storage device and a carrier storage device;

[0027] The feed port of the cooling device is connected to the heat exchange device, and is used to feed the gaseous dehydrogenation product after the heat exchange treatment into the cooling device, and use cooling water as the heat exchange medium to perform heat exchange cooling treatment;

[0028] The discharge port of the cooling device is connected to the separation device, and is used to separate the product after the heat exchange cooling treatment to obtain a liquid dehydrogenation organic carrier and hydrogen;

[0029] The separation device is connected to the hydrogen storage device and the carrier storage device, wherein the hydrogen storage device is used to store the hydrogen, and the carrier storage device is used to store the liquid dehydrogenated organic carrier.

[0030] Furthermore, the temperature of the liquid dehydrogenation organic carrier and the hydrogen is 15°C to 30°C.

[0031] By adopting the above method, the phase change temperature of the heat flow (gaseous dehydrogenation product) is appropriately increased from a relatively low temperature, thereby breaking the mismatch in heat exchange temperature between the gaseous dehydrogenation product and the liquid hydrogen-rich carrier due to bubble dew point slip, achieving better heat exchange, omitting the subsequent superheating treatment step, and greatly reducing the use of cold and hot utilities, thereby achieving the overall energy-saving effect of the organic liquid dehydrogenation process to the greatest extent.

[0032] It should be noted that after the gaseous dehydrogenation product is compressed and pressurized, the dew point temperature of the gaseous dehydrogenation organic carrier bubbles increases, and efficient heat exchange treatment is carried out with the liquid hydrogen-rich carrier.

[0033] In summary, the present application includes at least one of the following beneficial technical effects:

[0034] 1. The present application provides a waste heat recovery and utilization method and system for an organic liquid dehydrogenation process. During implementation, a compression device is used to compress and pressurize a gaseous dehydrogenation product to increase its bubble dew point temperature, thereby increasing the heat transfer temperature difference between the gaseous dehydrogenation product and the liquid hydrogen-rich carrier, exceeding the limit of the minimum heat transfer temperature difference, breaking the mismatch of the heat exchange temperature position between the two due to bubble dew point slippage, achieving better heat exchange, significantly improving the heat exchange rate of the gaseous dehydrogenation product and the liquid hydrogen-rich carrier, and achieving full coverage of the preheating requirements of the liquid hydrogen-rich carrier by the gaseous dehydrogenation product in the dehydrogenation process, so as to reduce the system utility usage, improve the comprehensive energy utilization rate of the dehydrogenation process, and the pressure of the hydrogen finally obtained is also improved. When input to the back-end application, it is helpful to significantly reduce the compression ratio, and achieve the pressure requirement through one-stage compression, so that the equipment investment and land occupation are greatly reduced;

[0035] 2. The present application provides a method for recovering and utilizing waste heat from an organic liquid dehydrogenation process, in which the waste heat of the gaseous dehydrogenation product after heat exchange is continued to be utilized for heat exchange with cooling water. The cooling water can be used as domestic water for residents, so that the domestic water for residents can be heated for heating. This achieves full utilization of the heat of the product of the organic liquid dehydrogenation process, increases the comprehensive thermal efficiency by more than 25%, reduces energy consumption by 10% to 15%, meets the requirements of energy conservation and consumption reduction, and makes the dehydrogenation process as a whole an energy terminal that can supply hydrogen and heat to the outside. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0037] Figure 1 The structure diagram of the reaction system for waste heat recovery and utilization of the organic liquid dehydrogenation process in the prior art proposed in the embodiment of the present application is shown;

[0038] Figure 2 The enthalpy diagram of the heat exchange process between the hydrogen-rich carrier and the dehydrogenation product in the prior art proposed in the embodiment of the present application is shown;

[0039] Figure 3 A flow chart of a waste heat recovery method of an organic liquid dehydrogenation process proposed in an embodiment of the present application is shown;

[0040] Figure 4 The enthalpy diagram of the heat exchange process between the liquid hydrogen-rich carrier and the gaseous dehydrogenation product proposed in the embodiment of the present application is shown;

[0041] Figure 5The structure diagram of the waste heat recovery system of the organic liquid dehydrogenation process proposed in the embodiment of the present application is shown;

[0042] Figure 6 The structure diagram of the reaction system for waste heat recovery and utilization of the organic liquid dehydrogenation process proposed in Example 1 of the present application is shown.

[0043] Description of reference numerals:

[0044] 1. Hydrogen-rich liquid storage device; 2. Heat exchange device; 3. Reaction device; 4. Compression device; 5. Cooling device; 6. Separation device; 7. Hydrogen storage device; 8. Carrier storage device. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] In the drawings, the size of the constituent elements, the thickness of the layer or the area may be exaggerated for the sake of clarity. Therefore, any implementation of the present disclosure is not necessarily limited to the size shown in the drawings, and the shapes and sizes of the components in the drawings do not reflect the true proportions. In addition, the drawings schematically show ideal examples, and any implementation of the present disclosure is not limited to the shapes or values ​​shown in the drawings.

[0047] In the related technology, the organic liquid dehydrogenation process refers to the catalytic dehydrogenation reaction of a liquid hydrogen-rich carrier under certain temperature conditions. The gaseous dehydrogenation product is condensed and then separated into gas and liquid. The separated hydrogen is transported to the hydrogen-using end for continued use. However, the process has problems such as high energy consumption and imperfect thermal management, which leads to low comprehensive energy efficiency and low hydrogen pressure level. Therefore, the prior art has carried out conventional thermal design for it. The following is a detailed description with 515 kg / h of methylcyclohexane as the injection volume. The reaction system is referenced Figure 1 :

[0048] Step 1, 515 kg / h of methylcyclohexane is injected as a hydrogen-rich carrier. At room temperature and pressure, the methylcyclohexane is pressurized to 0.3 MPa by a pump and then enters a product-carrier heat exchanger and is preheated to 248 °C.

[0049] Step 2, sending the methylcyclohexane at a temperature of 248°C into a superheater for superheating to a dehydrogenation reaction temperature of 350°C;

[0050] Step 3, after the methylcyclohexane reaches the dehydrogenation reaction temperature, it enters the reactor for dehydrogenation reaction, and the temperature of the dehydrogenation products (toluene and hydrogen) is 350°C. It is directly returned to the product-carrier heat exchanger without pressurization to exchange heat with the methylcyclohexane. The toluene and hydrogen after heat exchange enter the cooler for cooling treatment;

[0051] Step 4: The temperature of toluene and hydrogen after heat exchange is 89°C, and then cooled to 18°C ​​by a cooler, followed by gas-liquid separation. The pressure of the separated hydrogen is 0.2 MPa.

[0052] In the above process, the load of the product-carrier heat exchanger is 112 kw, the load of the superheater is 39 kw, the load of the reactor is 315 kw, and the load of the cooler is 60 kw. It can be obtained that in the conventional thermal design of the organic liquid dehydrogenation process, the heat exchange capacity between the dehydrogenation product and the hydrogen-rich carrier is small, the heat exchange efficiency is low, and the waste heat utilization rate is not high. And in terms of the grade of hot water generated, the heat source grade of this dehydrogenation product cannot be adjusted, and it is basically a fixed temperature, which is not conducive to practical application; and the pressure of the subsequently separated hydrogen is 0.2 MPa (absolute pressure). According to the subsequent hydrogen use scenario of 5 MPa, the compression ratio is 25, which is difficult to achieve through a first-stage compression, resulting in a significant increase in equipment investment and land occupation.

[0053] Based on the problems existing in conventional thermal design, the embodiment of the present application conducts a detailed analysis of the heat exchange process enthalpy of the hydrogen-rich carrier and the dehydrogenation product, as follows:

[0054] refer to Figure 2 Taking methylcyclohexane as an example, in the methylcyclohexane dehydrogenation process, the heat complementation between the hydrogen-rich carrier and the dehydrogenation product can be achieved in principle. However, after research, it was found that during the dehydrogenation of methylcyclohexane, the production of a large amount of hydrogen will cause the bubble dew point slip of another dehydrogenation product, toluene, which seriously affects the heat exchange between the dehydrogenation product and the hydrogen-rich carrier.

[0055] Specifically, the specific heat capacities of toluene and methylcyclohexane (1.8 J / g·K) are similar, and the dew point temperature of the former is 10 ℃~20 ℃ higher than the bubble point temperature of the latter at the same pressure, proving that high-efficiency heat exchange can be achieved between the two. However, in the actual dehydrogenation process, hydrogen and toluene are produced at the same time. When the molar amounts of hydrogen and toluene are at the same order of magnitude, the condensation process of toluene in the mixture of the two will change significantly. For example, the dew point temperature of toluene at 1 bar is about 112 ℃, while the dew point temperature of the mixture of hydrogen and toluene (molar ratio 1:1) at 1 bar is about 88 ℃, and the condensation process of the two is completely different. The pure component toluene will condense completely after the temperature drops below the dew point temperature, but the toluene in the mixture will continue to condense as the temperature decreases. Even at 25 ℃, about 4% of the toluene has not condensed. This special condensation process will change the heat exchange temperature between pure components, making the waste heat of a large amount of dehydrogenation products unable to be utilized by the hydrogen-rich carrier, and ultimately causing the heat exchange to be carried out only within a smaller temperature range, resulting in an insignificant reduction in the cooling and heating utilities of the organic liquid dehydrogenation process.

[0056] Based on this, the present application embodiment provides a method for recovering waste heat from an organic liquid dehydrogenation process, referring to Figure 3 , the specific steps include:

[0057] Step S1: compressing and pressurizing the gaseous dehydrogenation product outputted from the reaction device, and then using it for heat exchange with a liquid hydrogen-rich carrier, so that the liquid hydrogen-rich carrier is heated and vaporized to form a gaseous hydrogen-rich carrier;

[0058] Step S2: inputting the gaseous hydrogen-rich carrier into the reaction device for dehydrogenation treatment to obtain the gaseous dehydrogenation product;

[0059] Wherein, the difference between the dew point temperature of the gaseous dehydrogenation product after the compression and supercharging treatment and the dew point temperature of the liquid hydrogen-rich carrier is greater than the minimum heat transfer temperature difference;

[0060] The gaseous dehydrogenation product comprises a gaseous dehydrogenated organic carrier and hydrogen.

[0061] In specific implementation, the gaseous dehydrogenation product is compressed and pressurized, and the difference between its dew point temperature and the dew point temperature of the pressurized liquid hydrogen-rich carrier is controlled to be greater than the minimum heat transfer temperature difference, so that the heat transfer temperature difference between the two is enlarged. A larger heat transfer temperature difference means that more heat can be transferred during the heat exchange process, which greatly promotes the effective transfer of heat, thereby improving the efficiency of the heat exchange process.

[0062] When implementing it, refer to Figure 4The embodiment of the present application utilizes the characteristic that the bubble dew point temperature of the gaseous dehydrogenation product increases with increasing pressure, and first pressurizes the gaseous dehydrogenation product to appropriately increase the phase change temperature of the gaseous dehydrogenation product from a lower temperature, so as to break the mismatch of the heat exchange temperature between the liquid hydrogen-rich carrier and the gaseous hydrogen-poor product due to the bubble dew point slip. While the state of the liquid hydrogen-rich product remains unchanged, the distance between the two - that is, the actual heat transfer temperature difference becomes larger (this is because the upward movement of the bubble dew point means that the components in the gaseous dehydrogenation product (such as toluene) begin to condense at a higher temperature), and the heat transfer temperature difference is the driving force of heat transfer, which determines the efficiency and speed of heat transfer from the hot flow (gaseous dehydrogenation product) to the cold flow (liquid hydrogen-rich carrier). That is, when the heat transfer temperature difference becomes larger, the heat exchange between the liquid hydrogen-rich carrier and the gaseous dehydrogenation product can be increased, achieving Figure 4 The better heat exchange shown improves heat exchange efficiency, greatly reduces utility consumption in the dehydrogenation process, realizes energy self-supply during the operation of the device, improves the comprehensive energy utilization rate of the organic liquid dehydrogenation process, and reduces process energy consumption and operating costs.

[0063] In summary, using pressurized gaseous dehydrogenation products to preheat the liquid hydrogen-rich carrier not only recycles the waste heat of the gaseous dehydrogenation products and reduces the energy consumption of preheating the liquid hydrogen-rich carrier, but also solves the problem that the waste heat cannot cover the preheating demand of the liquid hydrogen-rich carrier due to the dew point slip of the gaseous dehydrogenation products. Compared with the traditional thermal design scheme, the preheating and superheating are combined into one equipment, which greatly saves the load of the preheating reaction section and reduces the investment cost.

[0064] In some embodiments, in step S2, the temperature of the dehydrogenation treatment is 300°C to 480°C; the pressure of the dehydrogenation treatment is 0.2 MPa to 0.4 MPa.

[0065] In some embodiments, the pressure of the gaseous dehydrogenation product after the compression and pressurization treatment is 0.5 MPa to 1.6 MPa;

[0066] The temperature of the gaseous hydrogen-rich carrier obtained by the heat exchange treatment is 350°C to 485°C;

[0067] The temperature of the gaseous dehydrogenation product after the compression and pressurization treatment is 70°C to 100°C after heat exchange treatment.

[0068] In specific implementation, the pressure of the gaseous dehydrogenation product can be 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa or 1 MPa. When the pressure of the gaseous dehydrogenation product increases, its bubble dew point temperature increases, and after heat exchange treatment, the liquid hydrogen-rich carrier can be completely vaporized and superheated, and the operation steps such as re-superheating treatment are omitted. The obtained gaseous hydrogen-rich carrier can meet the temperature and pressure required for dehydrogenation treatment.

[0069] In some embodiments, the compression ratio of the compression boosting process is 2-6.

[0070] In a specific implementation, the compression ratio of the compression and supercharging process can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6.

[0071] In some embodiments, the method further comprises:

[0072] The gaseous dehydrogenation product after the heat exchange treatment is collected and subjected to heat exchange cooling to liquefy the dehydrogenation organic carrier in the gaseous dehydrogenation product and separate it from the hydrogen.

[0073] In some embodiments, the pressure of the separated hydrogen is 0.5 MPa~1.6 MPa.

[0074] In specific implementation, the separated hydrogen has a certain adjustable range of pressure, which can meet the boosting requirements of the back-end usage scenarios. Taking the separated hydrogen pressure of 0.7 MPa as an example, according to the commonly used 5 MPa hydrogen boosting equipment, the compression ratio is 7, which greatly reduces the boosting ratio of the compressor at the application end compared with the traditional dehydrogenation process, effectively reduces the investment and land occupation of the compressor equipment, and also reduces the cost of the organic liquid dehydrogenation process, and enhances the strong correlation with the application end.

[0075] In some embodiments, the heat exchange cooling uses cooling water as the heat exchange medium.

[0076] In specific implementation, the gaseous dehydrogenation products treated by heat exchange can not only be cooled, but also be used to heat places that need low-level heat sources, such as heat medium water for heating residents. This is because after the gaseous dehydrogenation products are pressurized, they begin to exchange heat with the liquid hydrogen-rich carrier from a higher temperature, so that after they are completely vaporized and superheated, they still retain a relatively high temperature and can continue to exchange heat with domestic water as a low-temperature heat source, greatly increasing the availability of waste heat from the gaseous dehydrogenation products. The heated domestic water can be directly transported to residential areas for daily use by residents.

[0077] The present application also provides a waste heat recovery system for an organic liquid dehydrogenation process, and the system is applicable to a waste heat recovery method for the organic liquid dehydrogenation process, referring to Figure 5 , the system comprises: a hydrogen-rich liquid storage device 1, a heat exchange device 2, a reaction device 3 and a compression device 4;

[0078] The liquid outlet of the hydrogen-rich liquid storage device 1 is connected to the heat exchange device 2, and is used to transport the liquid hydrogen-rich carrier to the heat exchange device 2;

[0079] The feed port of the reaction device 3 is connected to the heat exchange device 2, and is used to pass the superheated gaseous hydrogen-rich carrier into the reaction device 3 for dehydrogenation treatment;

[0080] The discharge port of the reaction device 3 is connected to the compression device 4, and is used to send the gaseous dehydrogenation product into the compression device 4 for compression and pressurization treatment, so that the difference between the bubble dew point temperature of the gaseous dehydrogenation product and the bubble dew point temperature of the liquid hydrogen-rich carrier is greater than the minimum heat transfer temperature difference;

[0081] The compression device 4 is connected to the heat exchange device 2 and is used to transport the gaseous dehydrogenation product after compression and pressurization to the heat exchange device 2 to perform heat exchange treatment with the liquid hydrogen-rich carrier to obtain the superheated gaseous hydrogen-rich carrier.

[0082] In some embodiments, the system further comprises: a cooling device 5, a separation device 6, a hydrogen storage device 7 and a carrier storage device 8;

[0083] The feed port of the cooling device 5 is connected to the heat exchange device 2, and is used to feed the gaseous dehydrogenation product after the heat exchange treatment into the cooling device 5, and use cooling water as the heat exchange medium to perform heat exchange cooling treatment;

[0084] The discharge port of the cooling device 5 is connected to the separation device 6, which is used to separate the product after the heat exchange cooling treatment to obtain a liquid dehydrogenation organic carrier and hydrogen;

[0085] The separation device 6 is connected to the hydrogen storage device 7 and the carrier storage device 8, wherein the hydrogen storage device 7 is used to store the hydrogen, and the carrier storage device 8 is used to store the liquid dehydrogenated organic carrier.

[0086] In specific implementation, after the liquid hydrogen-rich carrier is extracted from the hydrogen-rich liquid storage device 1, it enters the heat exchange device 2 to perform heat exchange treatment with the pressurized gaseous dehydrogenation product, so that the liquid hydrogen-rich carrier is completely vaporized and the temperature can reach the temperature required for the dehydrogenation reaction;

[0087] The superheated gaseous hydrogen-rich carrier then enters the reaction device 3 to undergo a dehydrogenation reaction, and the gaseous dehydrogenation product is then compressed and pressurized by the compression device 4, and the difference between its dew point temperature and the dew point temperature of the liquid hydrogen-rich carrier is controlled to be greater than the minimum heat transfer temperature difference;

[0088] After the temperature of the pressurized gaseous dehydrogenation product is higher than the temperature required for the dehydrogenation reaction, it first enters the heat exchange device 2 to transfer heat to the newly produced liquid hydrogen-rich carrier, while its own temperature is reduced to 100 °C or below;

[0089] The dehydrogenation product with reduced temperature enters the cooling device 5, and then exchanges heat with cooling water (about 15°C) to heat the cooling water to above 40°C;

[0090] At the same time, its own temperature is reduced to 30°C or below, and finally it is passed into the separation device 6 for separation treatment. The separated hydrogen is discharged from the upper port of the separation device 6 and collected in the hydrogen storage device 7. The separated liquid dehydrogenation organic carrier is discharged from the lower port of the separation device 6 and collected in the carrier storage device 7 for subsequent treatment and use.

[0091] In summary, by utilizing the waste heat recovery and utilization system of the organic liquid dehydrogenation process provided in the embodiment of the present application, the gaseous dehydrogenation product is pressurized by the compression device 4, so that the waste heat of the gaseous dehydrogenation product can be more fully utilized, so that the comprehensive thermal efficiency of the organic liquid dehydrogenation process is increased by more than 25%, and the energy consumption is reduced by 10%~15%, thereby meeting the requirements of energy saving and consumption reduction, and solving the problem of difficulty in pressurizing the hydrogen supply of the separation product, thereby further improving the economy of the organic liquid dehydrogenation process.

[0092] In some embodiments, the temperature of the liquid dehydrogenated organic carrier and the hydrogen is 15°C to 30°C.

[0093] In order to enable those skilled in the art to better understand the present invention, the following is an explanation of a method and system for recovering waste heat from an organic liquid dehydrogenation process provided by the present invention through specific embodiments.

[0094] Example 1

[0095] Example 1 Application Figure 6 The reaction system is shown.

[0096] 1. With 515 kg / h of methylcyclohexane as the injection amount, at normal temperature and pressure, the methylcyclohexane is pressurized to 0.3 MPa by a pump and then enters the heat exchanger, preheated to the dehydrogenation reaction temperature of 350 °C, and then enters the reactor for dehydrogenation treatment to obtain toluene and hydrogen;

[0097] 2. Toluene and hydrogen enter the compressor at a temperature of 350 °C and are compressed and pressurized. The compression ratio is set to 5. The temperature of toluene after pressurization rises to 524 °C and the pressure is 1.5 MPa. The difference between its bubble dew point temperature and that of methylcyclohexane is greater than the minimum heat transfer temperature difference. After heat exchange treatment, the temperature of methylcyclohexane rises from 25 °C to 482 °C and is completely vaporized to obtain gaseous methylcyclohexane.

[0098] 3. After heat exchange treatment, the toluene still has low-grade heat (temperature is 107 ℃), which is sent to the cooler for heat exchange treatment with the cooling water (15 ℃) in the cooler, and the cooling water is heated to above 40 ℃ (adjustable according to the boost range), and the toluene and hydrogen themselves are cooled to 18 ℃;

[0099] 4. The toluene and hydrogen cooled to 18 °C enter the gas-liquid separation tank for separation treatment. The separated hydrogen is discharged from the upper port of the gas-liquid separation tank and stored in the hydrogen storage tank. The obtained liquid toluene is discharged from the lower port of the gas-liquid separation tank and stored in the carrier storage tank. The pressure of the separated hydrogen is 1.5 MPa.

[0100] After testing, in Example 1, the load of the heat exchanger is 208 kw, the power consumption of the compressor is 78 kw, the thermal power of the reactor is 258 kw, and the load of the cooler is 43 kw. Toluene is realized to exchange heat with methylcyclohexane from a higher temperature, and the energy self-supply ratio of methylcyclohexane preheating is increased from less than 75% to completely cover the energy consumption of the preheating section, which greatly improves the energy utilization rate of the process. Compared with the prior art, the compression equipment is pre-placed from the gas-liquid separation equipment to the reaction outlet, which not only solves the problem of the pressure mismatch between the hydrogen section and the hydrogen production end, but also solves the problem of large investment in compression equipment. And the cost of the compressor of the front-end superheater and the hydrogen terminal is reduced. It is calculated that the total load is reduced by more than 10%, which significantly reduces the supply of cold and hot utilities and reduces operating costs.

[0101] And through pressurized heat exchange, the quality of waste heat source of toluene can be improved, and it can be matched with the demand side and heat medium water for heating. Subsequently, liquid toluene and hydrogen are separated in a gas-liquid separation tank. The pressure of hydrogen after separation is 0.7MPa, which has a certain adjustable range of pressure. The hydrogen pressurization ratio of hydrogen-usable scenarios is greatly reduced, so that the investment and land occupation of the back-end pressurization equipment are highly competitive.

[0102] In summary, the waste heat recovery and utilization method and system of an organic liquid dehydrogenation process provided in the embodiment of the present application adopts the process technology scheme of pressurized gaseous dehydrogenation products, which can solve the problem of insufficient heat transfer temperature difference in the heat utilization process caused by the slip of the bubble dew point of the gaseous dehydrogenation product, and the low heat transfer driving force cannot meet the preheating requirements of the preheating section of the liquid hydrogen-rich carrier. Compared with the traditional thermal design scheme, the preheating and superheating are combined into one device, which greatly reduces the investment, and the energy saving after pressurization is 10%~15% lower than the conventional scheme, and the comprehensive energy utilization efficiency is increased by more than 25%. The system can also be used as an adjustable low-temperature heat source generator to carry out hydrogen-electricity-heat cogeneration with residential areas, and has a very rich application scenario.

[0103] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0104] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present application.

[0105] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

[0106] The above is a detailed introduction to the waste heat recovery method and system of an organic liquid dehydrogenation process provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for general technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for recovering waste heat from an organic liquid dehydrogenation process, characterized in that: The method comprises: S1. After compressing and pressurizing the gaseous dehydrogenation product outputted from the reaction device, the product is used for heat exchange with a liquid hydrogen-rich carrier, so that the liquid hydrogen-rich carrier is heated and vaporized to form a gaseous hydrogen-rich carrier; S2, inputting the gaseous hydrogen-rich carrier into the reaction device for dehydrogenation treatment to obtain the gaseous dehydrogenation product; Wherein, the difference between the dew point temperature of the gaseous dehydrogenation product after the compression and supercharging treatment and the dew point temperature of the liquid hydrogen-rich carrier is greater than the minimum heat transfer temperature difference; The gaseous dehydrogenation product comprises a gaseous dehydrogenated organic carrier and hydrogen.

2. The method for recovering waste heat from an organic liquid dehydrogenation process according to claim 1, characterized in that: In step S2, the temperature of the dehydrogenation treatment is 300°C to 480°C; the pressure of the dehydrogenation treatment is 0.2 MPa to 0.4 MPa.

3. The method for recovering waste heat from an organic liquid dehydrogenation process according to claim 1, characterized in that: The pressure of the gaseous dehydrogenation product after the compression and pressurization treatment is 0.5 MPa~1.6 MPa; The temperature of the gaseous hydrogen-rich carrier obtained by the heat exchange treatment is 350°C to 485°C; The temperature of the gaseous dehydrogenation product after the compression and pressurization treatment is 70°C to 100°C after heat exchange treatment.

4. The method for recovering waste heat from an organic liquid dehydrogenation process according to claim 1, characterized in that: The compression ratio of the compression and supercharging process is 2-6.

5. The method for recovering waste heat from an organic liquid dehydrogenation process according to claim 1, characterized in that: The method further comprises: The gaseous dehydrogenation product after the heat exchange treatment is collected and subjected to heat exchange cooling to liquefy the dehydrogenation organic carrier in the gaseous dehydrogenation product and separate it from the hydrogen.

6. The method for recovering waste heat from an organic liquid dehydrogenation process according to claim 5, characterized in that: The pressure of the separated hydrogen is 0.5 MPa~1.6 MPa.

7. The method for recovering waste heat from an organic liquid dehydrogenation process according to claim 5, characterized in that: The heat exchange cooling uses cooling water as the heat exchange medium.

8. A waste heat recovery system for an organic liquid dehydrogenation process, characterized in that: The system is applicable to the waste heat recovery and utilization method of the organic liquid dehydrogenation process according to any one of claims 1 to 7, and the system comprises: a hydrogen-rich liquid storage device, a heat exchange device, a reaction device and a compression device; The liquid outlet of the hydrogen-rich liquid storage device is connected to the heat exchange device for conveying liquid hydrogen-rich carrier to the heat exchange device; The feed port of the reaction device is connected to the heat exchange device, and is used to pass the superheated gaseous hydrogen-rich carrier into the reaction device for dehydrogenation treatment; The discharge port of the reaction device is connected to the compression device, and is used to send the gaseous dehydrogenation product into the compression device for compression and pressurization treatment, so that the difference between the bubble dew point temperature of the gaseous dehydrogenation product and the bubble dew point temperature of the liquid hydrogen-rich carrier is greater than the minimum heat transfer temperature difference; The compression device is connected to the heat exchange device and is used to transport the gaseous dehydrogenation product after compression and pressurization treatment to the heat exchange device for heat exchange treatment with the liquid hydrogen-rich carrier to obtain the superheated gaseous hydrogen-rich carrier.

9. The waste heat recovery and utilization system of the organic liquid dehydrogenation process according to claim 8, characterized in that: The system further comprises: a cooling device, a separation device, a hydrogen storage device and a carrier storage device; The feed port of the cooling device is connected to the heat exchange device, and is used to feed the gaseous dehydrogenation product after the heat exchange treatment into the cooling device, and use cooling water as the heat exchange medium to perform heat exchange cooling treatment; The discharge port of the cooling device is connected to the separation device, and is used to separate the product after the heat exchange cooling treatment to obtain a liquid dehydrogenation organic carrier and hydrogen; The separation device is connected to the hydrogen storage device and the carrier storage device, wherein the hydrogen storage device is used to store the hydrogen, and the carrier storage device is used to store the liquid dehydrogenated organic carrier.

10. The waste heat recovery and utilization system of the organic liquid dehydrogenation process according to claim 9, characterized in that: The temperature of the liquid dehydrogenation organic carrier and the hydrogen is 15°C to 30°C.

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