Segmented heat exchange energy saving method and system for use in an organic liquid dehydrogenation system

Abstract

The application provides a segmented heat exchange energy-saving method and system for an organic liquid dehydrogenation system. The method is based on temperature-accumulative heat exchange quantity (TQ) curve analysis. In view of the problem that the heat required by dehydrogenation raw materials is concentrated in the gasification phase change interval, and the heat release capacity of hydrogen-containing dehydrogenation products in the temperature zone is insufficient, an external heat source is inserted to supplement heat in the preheating process of the dehydrogenation raw materials, so as to make up for the local heat matching gap. At the same time, the high-temperature section heat of the dehydrogenation products is used to heat the high-temperature section of the dehydrogenation raw materials, and the medium and low-temperature section heat is used to heat the low-temperature section of the dehydrogenation raw materials, so as to realize efficient utilization of the waste heat in stages. The dehydrogenation products enter the external cooling unit only after completing all heat exchange. Compared with the traditional single-stage heat exchange design, the external heat source heating temperature can be reduced from above 360 DEG C to below 300 DEG C, the dependence on high-grade heat sources is significantly reduced, and the system energy-saving performance and operation flexibility are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy saving in chemical processes, in particular to a segmented heat exchange energy saving method and system for an organic liquid dehydrogenation system. BACKGROUND

[0002] In an organic liquid hydrogen storage system, the dehydrogenation process usually includes the steps of raw material preheating, reaction, product cooling, etc. The common energy saving design is to use the heat released by the dehydrogenation product to preheat the liquid dehydrogenation raw material to realize energy recovery.

[0003] However, since the dehydrogenation product contains a large amount of hydrogen (the volume fraction is usually more than 40%), its heat capacity is significantly lower than that of the liquid dehydrogenation raw material (methylcyclohexane or its mixture with toluene). At the same time, the liquid dehydrogenation raw material needs to go through a significant bubble point vaporization process during preheating, and a large amount of latent heat and sensible heat is needed near the bubble point.

[0004] In the temperature-cumulative heat exchange (TQ) curve analysis, this characteristic of "cold stream concentrated heat absorption, hot stream dispersed heat release" leads to local temperature crossing or no overlapping area between the two in the liquid dehydrogenation raw material vaporization temperature interval. Even if the total heat release of the dehydrogenation product is greater than the total heat requirement of the liquid dehydrogenation raw material, it cannot be matched by single heat exchange. Therefore, in the traditional single-stage primary heat exchange design, the raw material can only be heated to medium temperature, and still needs to rely on a high-temperature external heat source above 360℃ to heat it to the reaction temperature, resulting in strong dependence on high-grade heat sources and high operating costs. To solve this problem, a segmented heat exchange method based on thermodynamic matching optimization is needed to reduce the temperature requirement of external heat sources. SUMMARY

[0005] To solve the above problems, the present application provides a segmented heat exchange energy saving method and system for an organic liquid dehydrogenation system. Based on TQ curve analysis, it is found that in the liquid dehydrogenation raw material vaporization phase change temperature interval, the dehydrogenation product is insufficient in heat release due to the presence of hydrogen to meet the concentrated heat absorption requirement of the dehydrogenation raw material, forming a local heat matching gap. Therefore, the present application inserts an external heat source in this temperature interval for reheat, and realizes the step-by-step efficient use of the waste heat of the dehydrogenation product by reasonably allocating the heat exchange sequence.

[0006] In the first aspect, the present application provides a segmented heat exchange energy saving method for an organic liquid dehydrogenation system, comprising:

[0007] S1, using the medium and low temperature section heat of the dehydrogenation product to preliminarily preheat the dehydrogenation raw material, so that the temperature of the dehydrogenation raw material approaches or reaches the vaporization phase change temperature;

[0008] S2, inserting an external heat source to supplement heat in the temperature range in which the dehydrogenation raw material undergoes a gasification phase change, so as to make up for the heat gap between the cumulative heat absorption required by the dehydrogenation raw material gasification and the cumulative heat release of the dehydrogenation product in the temperature range;

[0009] S3, using the high-temperature section heat of the dehydrogenation product to perform final temperature rising on the dehydrogenation raw material which has completed the heat supplement, so as to make it close to or reach the dehydrogenation reaction temperature.

[0010] Optionally, the method further comprises:

[0011] S4, after the dehydrogenation product completes the entire heat exchange process, it enters a cold utility for cooling.

[0012] Optionally, the heat supplemented by the external heat source accounts for 15%-40% of the total heat required for preheating of the dehydrogenation raw material.

[0013] Optionally, the heat supply temperature of the external heat source is not higher than 300℃.

[0014] Optionally, the heat supply mode of the external heat source includes electric heating or heat exchange heating.

[0015] Optionally, the heat medium used in the heat exchange heating includes steam, heat-conducting oil or molten salt.

[0016] Optionally, the final temperature rising makes the temperature of the dehydrogenation raw material rise to not lower than 280℃.

[0017] The temperature difference between the dehydrogenation reaction temperature and the temperature of the dehydrogenation raw material after the final temperature rising is less than 20℃.

[0018] Optionally, the dehydrogenation product is a mixture after methylcyclohexane dehydrogenation reaction, and includes hydrogen, toluene and unreacted methylcyclohexane.

[0019] The dehydrogenation raw material is methylcyclohexane, or a mixture of methylcyclohexane and toluene.

[0020] In a second aspect, the present application provides a segmented heat exchange system used in an organic liquid dehydrogenation system, which is used to realize the segmented heat exchange energy-saving method of the first aspect, and comprises:

[0021] a first heat exchange unit (1), an external heating unit (3) and a second heat exchange unit (2);

[0022] The cold flow inlet of the first heat exchange unit (1) is connected to a 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).

[0023] The cold flow outlet of the external heating unit (3) is connected with the cold flow inlet of the second heat exchange unit (2);

[0024] The hot flow outlet of the second heat exchange unit (2) is connected with the hot flow inlet of the first heat exchange unit (1);

[0025] The first heat exchange unit (1) is used for transferring the heat of the medium-low temperature section of the dehydrogenation product to the dehydrogenation raw material, so that the dehydrogenation raw material is preliminarily preheated, and the temperature of the dehydrogenation raw material approaches or reaches the temperature of gasification phase change;

[0026] The external heating unit (3) is used for heating the dehydrogenation raw material in the temperature range of gasification phase change;

[0027] The second heat exchange unit (2) is used for transferring the heat of the high temperature section of the dehydrogenation product to the dehydrogenation raw material which has been heated, so that the dehydrogenation raw material is finally heated.

[0028] Optionally, the system further comprises an external cooling unit (5);

[0029] The hot flow inlet of the external cooling unit (5) is connected with the hot flow outlet of the first heat exchange unit (1);

[0030] The external cooling unit (5) is used for cooling the dehydrogenation product which has been completely heat-exchanged.

[0031] Optionally, the temperature of the dehydrogenation product before entering the external cooling unit (5) is not lower than 80℃.

[0032] Optionally, the external heating unit (3) is an electric heater, a heat conducting oil heat exchanger or a steam heater;

[0033] The heating temperature of the external heating unit (3) is not higher than 300℃.

[0034] Optionally, the first heat exchange unit (1) and the second heat exchange unit (2) are respectively composed of one or more heat exchangers through series connection or parallel connection.

[0035] Optionally, the system further comprises a separation unit (6);

[0036] The outlet of the external cooling unit (5) is connected with the inlet of the separation unit (6);

[0037] The separation unit (6) is used for separating hydrogen from the dehydrogenation product which is cooled to 25-30℃.

[0038] Optionally, the system further comprises a dehydrogenation reaction unit (4);

[0039] The product outlet of the dehydrogenation reaction unit (4) is connected with the hot stream inlet of the second heat exchange unit (2).

[0040] In summary, the present application includes at least one of the following beneficial technical effects:

[0041] The present application provides a segmented heat exchange energy-saving method and system for an organic liquid dehydrogenation system, which uses the high-temperature heat of the dehydrogenation product to heat the high-temperature section of the liquid dehydrogenation raw material, and uses the medium-low temperature heat of the dehydrogenation product to heat the low-temperature section of the liquid dehydrogenation raw material, thereby avoiding the energy level mismatch problem of "high-temperature heat source for low-temperature heating" or "low-temperature waste heat for high-temperature heating" in the traditional single-stage heat exchange, and improving the overall thermal efficiency of the system.

[0042] In the present application, the dehydrogenation product enters the external heat exchanger only after completing the entire heat exchange process (including the high-temperature section and the medium-low temperature section), thereby avoiding the waste of heat caused by early cooling and significantly reducing the cooling utility load.

[0043] The system provided by the present application has clear functions of each heat exchange unit and fixed connection sequence, which is convenient for engineering implementation and operation control; at the same time, the form of external heat source (such as electric heating, steam or heat conducting oil) can be flexibly selected according to the requirements of raw material flow, composition or reaction temperature, and various working conditions can be adapted. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0045] Figure 1 The temperature-cumulative heat exchange amount curve of the dehydrogenation product cooling and dehydrogenation raw material preheating process in the related art is shown;

[0046] Figure 2 The temperature-cumulative heat exchange amount curve of the dehydrogenation product-dehydrogenation raw material single-stage primary heat exchange process in the related art is shown;

[0047] Figure 3 The temperature-cumulative heat exchange amount curve of the dehydrogenation product-dehydrogenation raw material segmented heat exchange process proposed by the embodiments of the present application is shown;

[0048] Figure 4 The flow chart of the segmented heat exchange energy-saving method for the organic liquid dehydrogenation system proposed by the embodiments of the present application is shown;

[0049] Figure 5 The structure schematic diagram of the segmented heat exchange energy-saving system for the organic liquid dehydrogenation system proposed by the embodiments of the present application is shown;

[0050] Figure 6 Fig. 1 shows a schematic diagram of a single-stage primary heat exchange system for an organic liquid dehydrogenation process according to the present application.

[0051] Explanation of Reference Signs:

[0052] 1. first heat exchange unit; 11. first pipe;

[0053] 2. second heat exchange unit; 21. fourth pipe;

[0054] 3. external heating unit; 31. second pipe;

[0055] 4. dehydrogenation reaction unit; 41. third pipe;

[0056] 5. external cooling unit;

[0057] 6. separation unit;

[0058] 7. delivery pump; 71. fifth pipe;

[0059] 8. dehydrogenation reactor;

[0060] 9. first heat exchanger;

[0061] 10. second heat exchanger;

[0062] 101. third heat exchanger. DETAILED DESCRIPTION

[0063] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0064] In the drawings, the size of the constituent elements, the thickness of the layers, or the area may be exaggerated for the sake of clearness, and therefore, any one of the implementations of the present disclosure is not necessarily limited to the sizes as shown in the drawings. The shapes and the sizes of the components in the drawings do not reflect the actual ones. Furthermore, the drawings schematically show ideal examples, and any one of the implementations of the present disclosure is not limited to the shapes or the values shown in the drawings.

[0065] In the related art, methylcyclohexane is a typical hydrogen storage carrier in an organic liquid hydrogen storage system, and the dehydrogenation process thereof usually includes the steps of raw material feeding, preheating, reaction, product cooling, and separation. A common energy-saving design is to use the heat released by the dehydrogenation product cooling to preheat the liquid organic hydrogen storage raw material, so as to realize energy recovery.

[0066] However, since the dehydrogenation product contains a large amount of hydrogen (the volume fraction is usually more than 40%), its specific heat capacity is significantly lower than that of the liquid dehydrogenation raw material (methylcyclohexane or a mixture thereof with toluene). At the same time, the liquid dehydrogenation raw material needs to undergo a significant bubble point vaporization process during preheating, and the heat absorption is concentrated near the bubble point, including latent heat and sensible heat.

[0067] Figure 1 The temperature-cumulative heat transfer amount curve of the dehydrogenation product cooling and dehydrogenation raw material preheating process in the related art is shown, Figure 2 The temperature-cumulative heat transfer amount curve of the dehydrogenation product-dehydrogenation raw material single-stage primary heat exchange process in the related art is shown. As shown in Figure 1 And Figure 2 As shown in the temperature-cumulative heat transfer amount (TQ) curve analysis, this characteristic of "cold stream concentrated heat absorption and hot stream dispersed heat release" leads to local temperature crossing or no overlapping area in the raw material vaporization temperature interval, and even if the total heat release amount of the dehydrogenation product is greater than the total heat absorption amount of the liquid organic hydrogen storage raw material (i.e. the dehydrogenation raw material), it cannot be matched by single heat exchange. Therefore, in the traditional single-stage primary heat exchange design, the dehydrogenation raw material can only be heated to a medium temperature (such as 243℃), and still needs to rely on a high-temperature external heat source above 360℃ to heat it to the reaction temperature (300℃-400℃), resulting in strong dependence on high-grade heat sources and high operating cost.

[0068] To solve this problem, the embodiment of the present application proposes a segmented heat exchange energy-saving method based on thermodynamic matching optimization. Figure 3 The temperature-cumulative heat transfer amount curve of the dehydrogenation product-dehydrogenation raw material segmented heat exchange process proposed by the embodiment of the present application is shown, Figure 3 As shown in the temperature-cumulative heat transfer amount (TQ) curve analysis, this characteristic of "cold stream concentrated heat absorption and hot stream dispersed heat release" leads to local temperature crossing or no overlapping area in the raw material vaporization temperature interval, and even if the total heat release amount of the dehydrogenation product is greater than the total heat absorption amount of the liquid organic hydrogen storage raw material (i.e. the dehydrogenation raw material), it cannot be matched by single heat exchange. Therefore, in the traditional single-stage primary heat exchange design, the dehydrogenation raw material can only be heated to a medium temperature (such as 243℃), and still needs to rely on a high-temperature external heat source above 360℃ to heat it to the reaction temperature (300℃-400℃), resulting in strong dependence on high-grade heat sources and high operating cost.

[0069] Figure 4 The flow chart of the segmented heat exchange energy-saving method used in the organic liquid dehydrogenation system proposed by the embodiment of the present application is shown, Figure 4 As shown in the temperature-cumulative heat transfer amount (TQ) curve analysis, this characteristic of "cold stream concentrated heat absorption and hot stream dispersed heat release" leads to local temperature crossing or no overlapping area in the raw material vaporization temperature interval, and even if the total heat release amount of the dehydrogenation product is greater than the total heat absorption amount of the liquid organic hydrogen storage raw material (i.e. the dehydrogenation raw material), it cannot be matched by single heat exchange. Therefore, in the traditional single-stage primary heat exchange design, the dehydrogenation raw material can only be heated to a medium temperature (such as 243℃), and still needs to rely on a high-temperature external heat source above 360℃ to heat it to the reaction temperature (300℃-400℃), resulting in strong dependence on high-grade heat sources and high operating cost.

[0070] Step S1, the dehydrogenation raw material is preliminarily preheated by using the heat of the dehydrogenation product in the medium-low temperature section, so that the temperature of the dehydrogenation raw material approaches or reaches the temperature of the gasification phase change;

[0071] It should be noted that in step S1, when the heat exchange in the medium-low temperature section (preliminary preheating of the dehydrogenation raw material) is performed, the above-mentioned medium-low temperature dehydrogenation product is exchanged with the low temperature dehydrogenation raw material (temperature not higher than 50℃), and after the preliminary preheating is completed, the temperature of the dehydrogenation raw material is not lower than 100℃; preferably, the dehydrogenation raw material is preliminarily preheated to 100℃-160℃, and the temperature approaches or reaches the bubble point temperature of the dehydrogenation raw material; the medium-low temperature dehydrogenation product is cooled to not higher than 100℃;

[0072] In some embodiments, the dehydrogenation product is a mixture after the dehydrogenation reaction of methylcyclohexane, containing hydrogen, toluene and unreacted methylcyclohexane;

[0073] The dehydrogenation raw material is methylcyclohexane, or a mixture of methylcyclohexane and toluene.

[0074] The embodiments of the present application are aimed at the characteristics of the dehydrogenation product of methylcyclohexane, or a mixture of methylcyclohexane and toluene, that is, the proportion of hydrogen is high and the heat capacity is extremely low, and a segmented heat exchange is provided, which can effectively break through the limitations of the traditional single-stage primary heat exchange, and the external heat source only needs to provide medium-temperature supplemental heating (heat supply temperature below 300℃), thereby avoiding the use of high-temperature heat source above 360℃ in the traditional process.

[0075] Step S2, an external heat source is inserted to supplement heat in the temperature range in which the dehydrogenation raw material undergoes the gasification phase change, so as to make up for the heat gap between the cumulative heat absorption required by the gasification of the dehydrogenation raw material and the cumulative heat release of the dehydrogenation product in this temperature range;

[0076] It should be noted that in step S2, when the medium-temperature supplemental heating (making up the heat matching gap) is performed, after the preliminary preheating of the dehydrogenation raw material is completed, before the high-temperature section heat exchange is performed, the dehydrogenation raw material is heated by using the external heat source, so that the temperature of the dehydrogenation raw material is increased to 150℃-260℃; preferably, the temperature of the dehydrogenation raw material is increased to 250℃-260℃, so as to make up for the heat matching gap caused by the insufficient heat release of the hot stream in the gasification phase change range of the dehydrogenation raw material;

[0077] It should be further noted that in some embodiments, the heat supplied by the external heat source accounts for 15%-40% of the total preheating heat required by the dehydrogenation raw material;

[0078] The heat supply temperature of the external heat source is not higher than 300℃.

[0079] For example, the heat supplied by the external heat source accounts for 15%, 20%, 25%, 30%, 35%, 40% of the total heat required for preheating the dehydrogenation raw material; in the segmented heat exchange process of the embodiment of the present application, the heat supplied by the external heat source is controlled to reduce the dependence on the high-temperature external heat source, and the production goal of energy saving and emission reduction is achieved;

[0080] In some embodiments, the heat supply mode of the external heat source includes electric heating or heat exchange heating.

[0081] In some embodiments, the heat exchange heating uses a heat medium including steam, heat-conducting oil or molten salt.

[0082] It should be noted that the electric heating can be powered by a power grid, renewable energy or valley electricity storage.

[0083] The embodiment of the present application provides two optional modes of electric heating and heat exchange heating, and the energy supply mode is diversified, so that the optimal heating scheme can be selected according to the actual working condition.

[0084] Step S3, using the heat of the high-temperature section of the dehydrogenation product to perform final temperature rising on the dehydrogenation raw material which has completed the heat supplement, so that the dehydrogenation raw material approaches or reaches the dehydrogenation reaction temperature.

[0085] In some embodiments, the final temperature rising raises the temperature of the dehydrogenation raw material to not less than 280℃; and the temperature difference between the dehydrogenation reaction temperature and the temperature of the dehydrogenation raw material after the final temperature rising is less than 20℃.

[0086] It should be noted that in step S3, when the high-temperature section heat exchange (final temperature rising of the dehydrogenation raw material) is performed, the high-temperature dehydrogenation product (temperature not less than 350℃) is heat-exchanged with the dehydrogenation raw material which has completed the medium-temperature heat supplement, so that the dehydrogenation raw material is finally temperature-risen to not less than 300℃ to form a high-temperature dehydrogenation raw material; preferably, after the final temperature rising, the temperature of the dehydrogenation raw material is not less than 340℃, and the dehydrogenation product forms a medium-low-temperature dehydrogenation product.

[0087] In some embodiments, the method further comprises:

[0088] S4, after the dehydrogenation product completes the entire heat exchange process, the dehydrogenation product is cooled in a cold utility.

[0089] It should be noted that in step S4, when the delayed cooling and separation are performed, the dehydrogenation product is cooled by means of a cold utility after completing the heat exchange in steps S1 and S3 twice, so that the temperature of the dehydrogenation product is reduced to 25-30℃, and then hydrogen separation is performed.

[0090] It also needs to be explained that the cold utility is a circulating water or air cooling system; the embodiment of the present application introduces the cold utility after the dehydrogenation product completes all heat exchange processes, carries out heat exchange on the dehydrogenation product, recovers the waste heat of the dehydrogenation product below 100 DEG C through the refrigerant, and further reduces the total energy consumption of the system.

[0091] In summary, the embodiment of the present application makes the temperature change curve of the warming process of the low-temperature dehydrogenation raw material and the cooling process of the high-temperature dehydrogenation product more matched, especially adapts to the characteristics of large thermal capacity difference of the hydrogen-containing system. In addition, the external heat source only needs to provide mid-temperature section heat supplement, instead of the high-temperature heat source requirement of > 360 DEG C in the traditional process, thereby fundamentally reducing the heat supply grade. After the heat supply temperature of the external heat source is reduced, more easily obtained industrial waste heat or low-pressure steam can be used, the dependence on special high-temperature heating equipment (such as a high-temperature combustion furnace) is reduced, and the operation risk and control difficulty are reduced.

[0092] Figure 5 The structure diagram of the segmented heat exchange energy-saving system used in the organic liquid hydrogen storage system according to the embodiment of the present application is shown as Figure 5 The structure diagram of the segmented heat exchange energy-saving system used in the organic liquid hydrogen storage system according to the embodiment of the present application is shown as

[0093] The first heat exchange unit 1, the external heating unit 3 and the second heat exchange unit 2;

[0094] 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;

[0095] The cold flow outlet of the external heating unit 3 is connected to the cold flow inlet of the second heat exchange unit 2;

[0096] The hot flow outlet of the second heat exchange unit 2 is connected to the hot flow inlet of the first heat exchange unit 1;

[0097] The first heat exchange unit 1 is used for transferring the heat of the medium-low temperature section of the dehydrogenation product to the dehydrogenation raw material, so that the dehydrogenation raw material completes preliminary preheating, and the temperature of the dehydrogenation raw material approaches or reaches the temperature of the gasification phase change;

[0098] The external heating unit 3 is used for supplementing heat when the dehydrogenation raw material is in the temperature range of the gasification phase change;

[0099] The second heat exchange unit 2 is used for transferring the heat of the high-temperature section of the dehydrogenation product to the dehydrogenation raw material which has completed the heat supplement, so that the dehydrogenation raw material completes the final warming.

[0100] It needs to be explained that the first heat exchange unit 1 and the second heat exchange unit 2 can be a shell-and-tube heat exchanger, so that the dehydrogenation raw material and the dehydrogenation product can carry out efficient heat exchange without contacting each other;

[0101] As Figure 5As shown, the cold flow inlet provided on the first heat exchange unit 1 is connected with the feeding unit, for delivering the low-temperature dehydrogenation raw material to the first heat exchange unit 1, and the cold flow outlet is connected with the cold flow inlet of the external heating unit 3 through the first pipeline 11, for delivering the preliminarily preheated dehydrogenation raw material to the external heating unit 3;

[0102] In some embodiments, as shown in the figure, Figure 5 As shown, the system further comprises a dehydrogenation reaction unit 4;

[0103] The product outlet of the dehydrogenation reaction unit 4 is connected with the hot flow inlet of the second heat exchange unit 2.

[0104] It should be noted that the cold flow outlet provided on the external heating unit 3 is connected with the cold flow inlet of the second heat exchange unit 2 through the second pipeline 31, for delivering the reheated dehydrogenation raw material to the second heat exchange unit 2;

[0105] The hot flow inlet provided on the second heat exchange unit 2 is connected with the product outlet on the dehydrogenation reaction unit 4 through the third pipeline 41, for directly delivering the high-temperature dehydrogenation product generated by the dehydrogenation reaction unit 4 to the second heat exchange unit 2 to participate in heat exchange;

[0106] The hot flow outlet provided on the second heat exchange unit 2 is connected with the hot flow inlet of the first heat exchange unit 1 through the fourth pipeline 21, for delivering the dehydrogenation product which has completed the heat exchange in the high-temperature section to the first heat exchange unit 1, and using the low-temperature section heat therein to heat the low-temperature dehydrogenation raw material;

[0107] In some embodiments, as shown in the figure, Figure 5 As shown, the external heating unit 3 is an electric heater, a heat-conducting oil heat exchanger or a steam heater;

[0108] The heating temperature of the external heating unit 3 is not higher than 300℃.

[0109] It should be noted that the external heating unit 3 is connected with a heat utility, and the two constitute an external heat source; the heat utility is an electric power system or a heat exchange medium supply system, for providing electric power or heat exchange medium to the external heating unit 3; when the heat utility is a heat exchange medium supply system, the heat exchange medium includes steam or heat-conducting oil; at the same time, the inlet and outlet of the heat-conducting oil heat exchanger or the steam heater are respectively connected with the heat utility, so that the heat exchange medium enters the external heating unit 3 through the inlet to heat the dehydrogenation raw material, and the cooled heat exchange medium flows back to the heat utility through the outlet, for recycling the heat exchange medium.

[0110] In the embodiment of the present application, 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 heat circulation path, so that the low-temperature dehydrogenation product is used as the heat source of the first heat exchange unit 1 to recover the low-temperature waste heat of the dehydrogenation product; the external heating unit 3 is arranged between the two heat exchanges, and only needs to perform medium-temperature heat compensation on the preliminarily preheated dehydrogenation raw material, so as to greatly reduce the heating temperature (lower than 300 DEG C) of the external heat source; the second heat exchange unit 2 is connected with the dehydrogenation reaction unit 4 to realize instant heat capture of the high-temperature dehydrogenation product (greater than or equal to 350 DEG C), and avoid heat transmission and loss in the high-temperature section. The system structure arranged in the embodiment of the present application has independent control of each unit, improves the adaptability to the dehydrogenation raw material flow / constituent, and makes the system have higher energy recovery efficiency and better operation flexibility.

[0111] In some embodiments, as shown in FIG. 1, the system further comprises a delivery pump 7; Figure 5

[0112] The inlet of the delivery pump 7 is connected with the outlet of the feeding unit (any storage device), and the outlet of the delivery pump 7 is connected with the cold flow inlet of the first heat exchange unit 1 through a pipeline, so as to deliver the low-temperature (temperature lower than 30 DEG C) dehydrogenation raw material in the feeding unit to the first heat exchange unit 1.

[0113] In some embodiments, as shown in FIG. 1, the system further comprises an external cooling unit 5; Figure 5

[0114] The hot flow inlet of the external cooling unit 5 is connected with the hot flow outlet of the first heat exchange unit 1.

[0115] The external cooling unit 5 is used for cooling the dehydrogenation product after completing all heat exchanges.

[0116] It should be noted that, as shown in FIG. 1, the cooling unit is connected with a cold utility, and the cold utility is a circulating water or air cooling system. Figure 5

[0117] The inlet and outlet arranged on the cooling unit are respectively connected with the cold utility to realize circulating cooling of water or air.

[0118] In some embodiments, the temperature of the dehydrogenation product before entering the external cooling unit 5 is not lower than 80 DEG C.

[0119] In some embodiments, the dehydrogenation product after completing all heat exchanges is cooled to below 30 DEG C.

[0120] In the embodiment of the present application, the cooling unit is arranged to cool the dehydrogenation product (less than or equal to 100 DEG C) after completing all heat exchanges to less than or equal to 30 DEG C, so as to recover the low-temperature heat of the dehydrogenation product and improve the thermal efficiency of the system.

[0121] In some embodiments, as shown in FIG. 1,​​​Figure 5 As shown, the system further comprises a separation unit 6; an outlet of the external cooling unit 5 is connected with an inlet of the separation unit 6;

[0122] The separation unit 6 is used for separating hydrogen from the dehydrogenated product cooled to 25-30°C.

[0123] It should be noted that the separation unit 6 can be a gas-liquid separator.

[0124] After the dehydrogenated product cooled is separated by the separation unit 6, hydrogen, toluene and a small amount of unreacted methylcyclohexane are obtained.

[0125] In the embodiment of the present application, the dehydrogenated product is cooled to ≤30°C by the external cooling unit 5, so that the degree of liquefaction of the mixed gas is significantly improved, the separation unit 6 can extract high-purity hydrogen, and the additional energy consumption of gas compression and purification in the traditional process is reduced. At the same time, toluene and unreacted methylcyclohexane are fully liquefied under low-temperature environment, and the separation unit 6 can recover the liquid components, so that the raw material near-zero loss is realized.

[0126] In some embodiments, the first heat exchange unit 1 and the second heat exchange unit 2 are respectively composed of one or more heat exchangers in series or parallel.

[0127] It should be noted that the first heat exchange unit 1 can be composed of one or more heat exchangers in series or parallel; the second heat exchange unit 2 can be composed of one or more heat exchangers in series or parallel.

[0128] For example, the first heat exchange unit 1 can include two, four, six or eight heat exchangers.

[0129] The second heat exchange unit 2 can include two, three, five or seven heat exchangers; in the system provided by the embodiment of the present application, one or more heat exchangers in parallel or series can be used to realize each heat exchange process according to the requirements of material flow specifications, temperature difference control and the like.

[0130] In order for those skilled in the art to more clearly understand the present application, the segmented heat exchange energy-saving method and system used in the organic liquid dehydrogenation system according to the present application will be described in detail through the following embodiments.

[0131] Embodiment 1

[0132] Referring to Figure 6 the structure of the segmented heat exchange energy-saving system.

[0133] In this embodiment, the dehydrogenated product (hot stream) is cooled from 350°C to 25°C, and the dehydrogenated raw material (cold stream) is heated from 25°C to 340°C.

[0134] The specific process flow is as follows:

[0135] (1) The dehydrogenation raw material enters the first heat exchange unit 1, while the dehydrogenation product enters the first heat exchange unit 1, and the heat of the low-temperature section of the dehydrogenation product is used to preliminarily preheat the dehydrogenation raw material, so that the temperature of the dehydrogenation raw material is raised from 25°C to 147°C (the temperature is close to or reaches the temperature of the gasification phase change), and the temperature of the dehydrogenation product is reduced from 274°C to 82°C;

[0136] (2) The preliminarily preheated dehydrogenation raw material then enters the external heating unit 3, and the dehydrogenation raw material is heated by the electric heater in the temperature range of the gasification phase change to make up for the heat gap between the cumulative heat absorption required by the dehydrogenation raw material and the cumulative heat release of the dehydrogenation product in the temperature range, so that the temperature of the dehydrogenation raw material is raised from 147°C to 258°C;

[0137] (3) The dehydrogenation raw material after heating enters the second heat exchange unit 2, and the high-temperature dehydrogenation product is discharged from the dehydrogenation reaction unit 4 and enters the second heat exchange unit 2, and the heat of the high-temperature section of the dehydrogenation product is used to finally heat the dehydrogenation raw material, so that the temperature of the dehydrogenation raw material reaches 340°C (the temperature is close to or reaches the dehydrogenation reaction temperature), and then is transported to the dehydrogenation reaction unit 4 for dehydrogenation reaction; the temperature of the high-temperature dehydrogenation product is reduced from 350°C to 274°C, forming a low-temperature dehydrogenation product, which is then transported to the first heat exchange unit 1 to continue to participate in subsequent heat exchange;

[0138] (4) The dehydrogenation product after completing all heat exchange processes enters the external cooling unit 5, and is cooled to 25°C by using cold utilities (circulating water), and then is transported to the separation unit 6 for hydrogen separation treatment, to obtain hydrogen, toluene and a small amount of methylcyclohexane.

[0139] It should be noted that the dehydrogenation raw material can only reach 340°C after final heating, because the last preheating is provided by the dehydrogenation product, and the upper limit of the preheating temperature is limited to meet the minimum heat transfer temperature difference of 10°C. The final required reaction temperature of 350°C of the dehydrogenation raw material is completed by internal heating of the dehydrogenation reaction unit 4.

[0140] In the segmented heat exchange process of Example 1, the total heat required for preheating the dehydrogenation raw material is 4388kW, the total heat released during the cooling process of the dehydrogenation product is 4957kW, the heat load of the first heat exchange unit 1 is 2388kW, the heating unit provides 1071kW, the heat load of the second heat exchange unit 2 is 929kW, and the cold utilities required by the external cooling unit 5 carry away 1640kW of heat.

[0141] Comparative Example 1

[0142] Referring to the conventional single-stage primary heat exchange system shown in ​ .

[0143] Comparative Example 1 is a traditional single-stage primary heat exchange design, in which the dehydrogenation product is cooled from 350℃ to 25℃, and the dehydrogenation feedstock is heated from 25℃ to 340℃.

[0144] The specific process is as follows:

[0145] (1) The dehydrogenation product from the reactor outlet enters the first heat exchanger 9, and the temperature is reduced from 350℃ to 83℃ after heat exchange with the dehydrogenation feedstock; the dehydrogenation feedstock is heated from 25℃ to 243℃ in the first heat exchanger 9;

[0146] (2) The dehydrogenation feedstock then enters the second heat exchanger 10, and is heated to 340℃ by an external heat source;

[0147] (3) The dehydrogenation product from the first heat exchanger 9 outlet enters the third heat exchanger 101, and is cooled to 25℃ by circulating water.

[0148] In this process, the actual heat exchange amount of the first heat exchanger 9 is 3296kW, the external heat source required by the second heat exchanger 10 is 1212kW, and the cooling utility load of the third heat exchanger 101 is 1661kW.

[0149] Since the feedstock can only be heated to 243℃ in the first heat exchanger 9, it still needs to be heated to 340℃ by the second heat exchanger 10, so the temperature of the heat source required by the second heat exchanger 10 must be higher than 360℃ to meet the heat transfer driving temperature difference requirement.

[0150] However, in the embodiment 1 of the present application, the temperature required by the external heat source (external heating unit 3) is only above 157℃ under the premise of meeting the minimum heat transfer temperature difference of 10℃, which is significantly lower than that of Comparative Example 1.

[0151] In summary, the present application realizes a more optimal thermodynamic property matching between the cold and hot streams through the segmented heat exchange design. Compared with the traditional single-stage primary heat exchange, the heating temperature of the external heat source is reduced from above 360℃ to below 300℃, and the heating requirement of the feedstock can be met without relying on a high-temperature external heat source, which significantly improves the energy saving and operation flexibility of the system, is suitable for various dehydrogenation reaction conditions, and has good industrial application prospect and promotion value.

[0152] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the embodiments can be referred to each other.

[0153] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to include the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present application.

[0154] Finally, it is also necessary to point out that in this text, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "contain" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or terminal device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or terminal device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or terminal device including the element.

[0155] The above provides a segmented heat exchange energy saving method and system for an organic liquid dehydrogenation system. The principles and implementation modes of the present application are described by applying specific examples in this text. The above example is only used to help understand the method and core idea of the present application. Meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In summary, the content of the specification should not be understood as a limitation of the present 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. The system for implementing the segmented heat exchange energy-saving method 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.

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 process raises the temperature of the dehydrogenation feedstock to at least 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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