CN114573415A - Method and device for separating coupling type alkane catalytic dehydrogenation reaction product - Google Patents

Method and device for separating coupling type alkane catalytic dehydrogenation reaction product Download PDF

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CN114573415A
CN114573415A CN202011372191.6A CN202011372191A CN114573415A CN 114573415 A CN114573415 A CN 114573415A CN 202011372191 A CN202011372191 A CN 202011372191A CN 114573415 A CN114573415 A CN 114573415A
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gas
box system
cold box
separation
cold
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CN114573415B (en
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吴笛
吴铁锁
田靖
丁干红
吕建宁
李延生
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Wison Engineering Ltd
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    • C07—ORGANIC CHEMISTRY
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    • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
    • C07C5/32—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen
    • C07C5/327—Formation of non-aromatic carbon-to-carbon double bonds only
    • C07C5/333—Catalytic processes
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    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the feed stream
    • F25J3/062—Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
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    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
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    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
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    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
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    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/0655—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of hydrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
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    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/12—Refinery or petrochemical off-gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/60—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being (a mixture of) hydrocarbons
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
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    • F25J2260/00—Coupling of processes or apparatus to other units; Integrated schemes
    • F25J2260/02—Integration in an installation for exchanging heat, e.g. for waste heat recovery
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/12—External refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/18—External refrigeration with incorporated cascade loop
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    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/60—Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
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    • F25J2270/00—Refrigeration techniques used
    • F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
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    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
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Abstract

The invention relates to a method and a device for separating coupling type alkane catalytic dehydrogenation reaction products, which are characterized in that product gas at the outlet of an alkane dehydrogenation reactor is input into a cold box system to obtain cooled products; inputting the cooled product into a gas-liquid separation tank with N stages connected in series for gas-liquid separation, and then inputting the gas-phase product obtained from the 1 st to N-1 st stages into a cold box system again; the liquid phase products obtained from the 1-N stages are collected and then reheated and sent out of a boundary area, and then the separation of the products with different carbon numbers of the liquid phase products is realized through a separation tower; mixing the circulating gas obtained from the top of the N-stage separation tank with fresh propane according to a preset hydrogen/hydrocarbon ratio through M stages, throttling and evaporating in a cold box system, and providing cold energy for the cold box system; introducing tail gas at the top of the deethanizer into a cold box system, and providing cold energy for the cold box system; the cold energy of the cold box system is also from an external refrigeration cycle system. The invention can reduce the energy consumption of separation and product loss, and has simple process flow, environmental protection, compact equipment and convenient and quick start/stop.

Description

Separation method and device for coupling type alkane catalytic dehydrogenation reaction product
Technical Field
The invention relates to the technical field of chemical separation, in particular to a method and a device for separating coupling type alkane catalytic dehydrogenation reaction products.
Background
The alkane can generate dehydrogenation reaction in the presence of the catalyst to generate olefin and hydrogen with higher added value. Among the various olefins, propylene is an important petrochemical feedstock. The method is mainly used for producing dozens of petrochemical products and raw materials such as polypropylene, propylene oxide, acrylic acid, acrylonitrile, alkylate oil, high-octane gasoline blend and the like. In recent years, the demand of propylene in China is continuously and rapidly increased due to the rapid development of various downstream chemical products of propylene.
Propylene has long been derived primarily from naphtha steam cracking processes and catalytic cracking processes for petroleum refining. In recent years, some new, economical techniques for producing propylene have attracted attention and have been successfully commercialized against the background of the growing demand of the downstream market for propylene. The method comprises a methanol-to-olefin (MTO) process, a methanol-to-propylene (MTP) process, an Olefin Cracking Process (OCP) and a propane dehydrogenation-to-propylene Process (PDH). Among the various processes for producing propylene, propane dehydrogenation for directionally producing propylene by using propane has been greatly successful because of its simple process flow and excellent economy. In recent years, more than twenty sets of propane dehydrogenation devices are built and put into production in China, and the scale of the produced propylene exceeds 1200 million tons/year. Therefore, propane dehydrogenation technology is currently the most competitive propylene production process, and the market share is continuously expanding.
The propane dehydrogenation reaction product mainly contains hydrogen and carbon three, and also contains a small amount of methane, carbon two, nitrogen and the like. Methane and part of the carbon dioxide come from the by-products of propane dehydrogenation, part of the carbon dioxide comes from the raw material propane, and nitrogen comes from the regeneration process. The reactor outlet material is cooled, compressed, dried and then fed to a separation system where the mixture of propylene and unreacted propane is gradually condensed in a cold box and propylene is recovered in a downstream rectification unit and propane is recycled back to the reactor. Because the propane dehydrogenation reaction product contains a large amount of hydrogen, the separation of hydrogen and carbon three needs to be realized at a cryogenic temperature. After the hydrogen-rich gas is reheated, pure hydrogen products are obtained through PSA purification, and tail gas adsorbed by PSA is used as fuel gas for outward transportation.
The existing industrialized separation process of propane dehydrogenation reaction products adopts a low-temperature cryogenic process to realize the separation of light components and C, and the reaction products are gradually cooled to-95 to-125 ℃ in a plate-fin heat exchanger. According to the composition difference condition of reaction products of different processes, the cold quantity required by separation is usually obtained by adopting double-expansion refrigeration or external single-component refrigeration, the process is relatively complex, and the recovery rate of carbon III is limited by the condition of the reaction products or the lowest refrigeration temperature obtained by external refrigeration. The energy consumption of the entire separation plant and the investment in equipment are relatively high. In addition, the carbon three product obtained by the separation system necessarily contains a certain amount of hydrogen and carbon two, and the light component is separated by the deethanizer and then is sent to the propylene tower to realize the separation of polymerization grade propylene and propane. At present, the industry provides temperature-matched cold for the top of the deethanizer by independently configuring a set of refrigerating units to realize partial condensation of the gas phase at the top of the deethanizer. Thus, the whole separation system has complex units and puts high requirements on the smooth operation of the device.
Disclosure of Invention
The invention provides a method and a device for separating coupling type alkane catalytic dehydrogenation reaction products, which overcome the defects of poor separation effect, high energy consumption, low carbon recovery rate, complex unit and the like of propane dehydrogenation reaction gas in the prior art.
The purpose of the invention can be realized by the following technical scheme:
the inventor finds in research that the raw material propane of the propane dehydrogenation device is stored in a low-temperature liquid state, the liquid raw material propane needs to be gasified and then enters a reactor according to the characteristics of alkane catalytic dehydrogenation reaction and the feeding requirement, and the gasification of the raw material needs to absorb a large amount of heat, so that the gasification of the raw material propane can be coupled with a separation system, cold energy is provided for the separation system, and the optimized matching of energy is realized; in addition, the tail gas at the top of the deethanizer contains a large amount of carbon dioxide, methane and a small amount of hydrogen, the pressure is high (can reach 2.25 MPaG-2.85 MPaG), and the cold energy at the temperature of-100 ℃ to-160 ℃ can be generated after precooling, depressurization and throttling, so that the part of the cold energy can be coupled with a separation system, the optimized matching of energy is realized, and the energy consumption of the separation system is saved.
Meanwhile, the mixed refrigerant refrigeration method can effectively reduce the cryogenic separation temperature and improve the recovery rate of the carbon product III. The three cold flows are skillfully and effectively coupled into the separation system, the cold required for separation is provided for the separation system together by changing and adjusting the original trend and the connection form of the materials and coupling the precooling refrigeration cycle and the mixed refrigerant copious cooling refrigeration cycle according to the temperature grade, the generated reaction gas does not need throttling expansion refrigeration, and the temperature grade from minus 160 ℃ to minus 40 ℃ is finally realized only by adjusting reasonable refrigerant proportion and operation parameters. The aim of fully recovering the carbon three products is achieved in advance of reducing the equipment investment.
The separation method of the coupled alkane catalytic dehydrogenation reaction product comprises the following steps:
inputting reaction product gas at the outlet of the alkane catalytic dehydrogenation reactor into a cold box system to obtain a cooled product;
inputting the cooled product into N-stage gas-liquid separation tanks connected in series for gas-liquid separation, and then:
the gas phase product obtained from the 1 st to the N-1 st level is input into a cold box system again and is cooled to the temperature of-95 ℃ to-160 ℃, preferably-115 ℃ to-145 ℃, and more preferably-120 ℃ to-138 ℃;
the liquid phase products obtained from the 1-N stages are collected and then reheated and sent out of a cold box system, and then the separation of the products with different carbon numbers of the liquid phase products is realized through a separation tower;
mixing the circulating gas obtained from the top of the Nth-stage gas-liquid separation tank with fresh propane according to a preset hydrogen/hydrocarbon ratio by M stages, throttling and evaporating in a cold box system, providing cold energy for the cold box system, reheating and then sending out the cold box system, wherein M is less than or equal to N;
the dry gas obtained from the top of the Nth-stage gas-liquid separation tank is reheated in the cold box system and then is sent out of the cold box system;
introducing tail gas at the top of the deethanizer into a cold box system, cooling the tail gas to the temperature of the Nth-stage separation through a multi-stage cold box, reducing the pressure, throttling the tail gas to 125-400 kPaG, preferably 200-375 kPaG, returning the tail gas to the cold box, reheating the tail gas to 15-45 ℃, and sending the tail gas out of the cold box system;
the cold energy of the cold box system is also from an external refrigeration cycle system.
Furthermore, the series stages of the heat exchangers of the cold box system are equal to and matched with the stages of the N-stage separation tanks step by step, the cold box system comprises a precooling section formed by one or more stages, and a deep cooling section formed by the rest.
Furthermore, 60-100% of the fresh propane flow is distributed to the pre-cooling section, and the rest is distributed to the deep cooling section, and the distributed flow and the fresh propane temperature grade are matched according to negative correlation.
Further, part of cold energy of the cold box system is from cold energy generated after the fresh propane and the recycle gas are mixed in a multistage mode, throttling gasification evaporation is carried out, and tail gas at the top of the deethanizer is cooled and throttled; after extensive research, the inventor finds that 60% -100% of the fresh propane flow needs to be distributed to the pre-cooling section in order to achieve the optimal energy coupling effect, and the principle that the distribution is gradually reduced along with the increase of the temperature grade is satisfied. The tail gas at the top of the deethanizer tower is precooled to the temperature of the Nth-stage separation in a multistage mode through a cold box system, throttled and returned to the cold box, reheated to 15-45 ℃ and discharged out of the battery limit.
Further, liquid-phase products of the gas-liquid separation tanks at all levels return to the cold box system by utilizing the pressure of the liquid-phase products, are reheated and gathered, then enter the liquid product tank, and then are pumped into the cold box system again to be reheated and enter the deethanizer to realize the separation of hydrogen, carbon one, carbon two and carbon three.
Further, the external refrigeration cycle system includes: a precooling refrigeration circulation system for providing cold energy for the precooling section and a copious cooling refrigeration circulation system for providing cold energy for the copious cooling section.
Further, N is more than 2, preferably 3-5, and more preferably 3-4.
Further, the refrigerant in the precooling refrigeration cycle system is one or a combination of more of ammonia, ethane, ethylene, propylene, propane, butane and pentane;
the refrigerant in the cryogenic refrigeration cycle system is a combination of a plurality of nitrogen, methane, ethane, ethylene, propane, propylene and butane.
Further, the circulating gas flow rate is matched with a preset hydrogen/hydrocarbon ratio in a proportional mode;
when the preset hydrogen/hydrocarbon ratio is zero, the circulating gas flow is set to zero, and the fresh propane is throttled and evaporated only at the corresponding stage number of the pre-cooling section.
Further, the tail gas at the top of the deethanizer is cooled to the temperature of the Nth-stage separation by the cold box system, throttled and returned to the cold box system, and sent out of the cold box system after reheating.
The separation device of the coupling type alkane catalytic dehydrogenation reaction product comprises a cold box system, a precooling refrigeration circulation system and a cryogenic refrigeration circulation system, wherein the separation device specifically comprises the following components:
the cold box system is respectively connected with an outlet of the alkane catalytic dehydrogenation reactor and a tail gas outlet at the top of the separation tower, and is connected with a fresh propane storage tank, and the cold box system comprises a pre-cooling section and a deep cooling section;
the precooling refrigeration cycle system is connected with the precooling section in a heat exchange manner and provides cold energy for the precooling, cooling and separating process of the reaction product gas at the outlet of the alkane catalytic dehydrogenation reactor;
the cryogenic refrigeration circulating system is connected with the cryogenic section in a heat exchange manner and provides cold energy for the cryogenic cooling separation process of the reaction product gas at the outlet of the alkane catalytic dehydrogenation reactor;
and the N-stage separation tank is connected with the cold box system and is matched with the cold box system step by step, the gas phase at the top of the N-stage separation tank is divided into two streams of dry gas and circulating gas, the circulating gas and fresh propane are mixed by M stages according to a preset hydrogen/hydrocarbon ratio and are input into the cold box system, wherein M is less than or equal to N, and the outlets of the liquid-phase products obtained from 1-N stages of the separation tank are sequentially connected with the liquid product tank and the separation tower, so that the separation of the products with different carbon numbers is realized.
Further, the tank top of the liquid product tank is also provided with a falling film condenser;
the separation tower is a deethanizer;
the cold box system comprises a multi-stage plate-fin heat exchanger.
Furthermore, the precooling refrigeration cycle system is also in heat exchange connection with a condenser, a falling film condenser and a cryogenic refrigeration cycle system of the deethanizer respectively.
For convenience of illustration, the propane dehydrogenation reaction product is used as an example, but most of the alkane dehydrogenation reaction products are used in the present method and apparatus for separating alkane catalytic dehydrogenation reaction products.
Compared with the prior art, the invention has the following technical advantages:
1) the energy consumption of separation is saved: the process flow of the invention achieves the purpose of saving separation energy consumption by adopting the following points: 1. the product of the propane dehydrogenation reactor is gradually condensed in a cold box system and then needs to be extracted for a plurality of times, the product enters a separation tank, a liquid phase product is separated, a gas phase returns to the cold box for further condensation, and then the gas phase enters the next-stage separation tank. The design can play a role in reducing the separation energy consumption and reducing the energy required by an external refrigeration cycle system; 2. the reaction raw material propane is mixed with the circulating gas (rich hydrogen) at a plurality of positions and then is throttled and gasified to generate cold energy, and the cold energy of the raw material is brought into a cold box system to reduce the cold energy required to be provided by an external refrigeration circulating system; 3. introducing tail gas of the deethanizer into a cold box system, reducing the temperature and throttling to generate low temperature, providing cold energy for a separation system, and saving energy consumption for separation; 4. the mixed refrigerant is adopted for refrigeration, the temperature difference in the whole heat transfer process is ensured to be small, the accurate matching of the cold quantity required by condensation of the reaction product and the cold quantity generated by refrigeration can be realized, and the aims of cold quantity matching and equivalent temperature are fulfilled, so that the irreversibility and the temperature in the heat transfer process are reduced
Figure BDA0002807074630000051
Loss, and finally the aim of reducing the separation energy consumption is achieved.
2) The loss of carbon three in the hydrogen-rich gas is reduced: in the separation process of the propane dehydrogenation reaction product, the final-stage cryogenic temperature of the reaction product has positive correlation with the loss of the carbon three. The mixed refrigerant is used as the refrigerant of the cryogenic refrigeration cycle system, the expected cryogenic temperature can be achieved by selecting and optimizing the components of the refrigerant formula, and compared with the existing refrigeration cycle adopting ethylene single refrigerant, the limit of the lowest refrigeration temperature of ethylene refrigeration can be broken through, and the cold energy with the temperature below 100 ℃ below zero is generated, so that the purpose of reducing the loss rate of the carbon-carbon product is achieved. If compared with the existing refrigeration process adopting double expansion, the refrigeration temperature of the expander can be broken through, the temperature lower than that of the expander process is generated, and the purpose of reducing the loss rate of the carbon three product is also achieved.
3) The equipment and the process are more compact, and the investment is reduced: compared with the prior process, the process has the advantages that the cold energy of the overhead condenser of the deethanizer is integrated into the precooling refrigeration cycle system, so that a refrigerating unit can be prevented from being independently arranged, the process is more simplified and compact, the equipment investment of the whole propane dehydrogenation device is reduced, and the economical efficiency is improved. In addition, if the mixed refrigerant refrigeration cycle system is adopted for precooling and copious cooling to provide cold for the separation system, the respective refrigerant formulas of the two refrigeration cycle systems can be adjusted to enable the power consumption of the two compressors to be equal, the power devices with the same specification can be adopted, the complete difficulty and the operation cost of the compressor unit can be reduced, and the overall economy and the operability of the device can be improved.
4) The cold box system operates more smoothly: because the raw material propane is subjected to multi-stage distribution in the cold box system according to a certain temperature grade matching principle, the complete gasification of the propane in the cold box system is ensured, and the cold energy is provided; the phenomenon that the separation system is stopped due to vicious circle that the heat exchange area is reduced and the gasification rate is reduced because the flow channel is submerged due to accumulation of unvaporized propane in the flow channel is avoided.
5) The process is more environment-friendly: because the refrigeration capacity of the raw material propane and the tail gas at the top of the deethanizer is coupled in the traditional refrigeration cycle system, the refrigeration capacity required to be provided by the external refrigeration cycle system is reduced, and the refrigerant quantity is reduced; when the device is stopped, the discharge amount of the torch is reduced, the amount of generated greenhouse gas is reduced, and the discharge time is shorter, so that the process is more environment-friendly. Meanwhile, the reduction of the discharge amount can also reduce the design load of a torch system, and reduce the equipment investment and the occupied area.
6) The driving is more concise, stable and quick: because a precooling and deep cooling double-circulation refrigerating system is adopted to provide cold energy for the separating device, the precooling circulating system is started firstly when the vehicle is started to provide precooling cold energy for the cold box system, and the deep cooling circulating system is started after the vehicle is stabilized to provide deep cooling cold energy for the cold box system. The process is safe and simple and is easy to operate. The driving process is more stable and convenient, the driving efficiency is high, the driving time is shortened, and the whole operability of the device is improved.
Drawings
FIG. 1 is a schematic diagram of the process of the present invention;
FIG. 2 is a schematic flow chart of an embodiment 1 of the present invention;
FIG. 3 is a schematic flow chart of an embodiment 2 of the present invention;
FIG. 4 is a schematic flow chart of embodiment 3 of the present invention;
FIG. 5 is a schematic flow chart of an embodiment 4 of the present invention;
FIG. 6 is a schematic flow chart of an embodiment 5 of the present invention;
fig. 7 is a schematic flow diagram of comparative example 1.
The content represented by each reference numeral is specifically:
plate-fin heat exchanger: EX-101, EX-102, EX-103, EX-104; the gas-liquid separation tanks are V-101, V-102, V-103, V-104 and V-201; a carbon three product tank V-105; a falling film condenser E-201; a deethanizer overhead condenser E-301; and a carbon three product pump P-101A/B.
Detailed Description
The method and the device for separating the coupled propane dehydrogenation reaction product provided in the embodiment can be realized by adopting the following technical scheme:
and (3) pretreating reaction product gas at the outlet of the propane dehydrogenation reactor by cooling, compressing, purifying, filtering and the like, then feeding the reaction product gas into a separation system, cooling the reaction product gas in a cold box system of the separation system, pumping the cooled reaction product gas out, feeding the cooled reaction product gas into a gas-liquid separation tank for gas-liquid separation, and continuously feeding the gas phase into the cold box system for cooling to the next stage of gas-liquid separation until the expected cooling temperature is reached and the recovery rate requirement of the C-C product is met. The gas phase (rich in hydrogen) at the top of the last-stage separation tank is divided into two material flows of dry gas and circulating gas, the circulating gas is mixed with fresh propane according to a certain hydrogen/hydrocarbon ratio through M stages (M is less than or equal to N), the mixture is throttled and evaporated in a cold box system to provide cold energy, and the cold energy is reheated and then sent out of a boundary area of a separation system to enter a reactor; the dry gas is reheated and then sent out of the boundary area. If the preset hydrogen/hydrocarbon ratio is zero, no recycle gas is required and fresh propane need only be throttle evaporated in the pre-cooling section. And cooling the tail gas at the top of the deethanizer tower to the temperature of the Nth-stage separation by a heat exchanger in a multi-stage cold box system, throttling and returning the tail gas to the cold box system, reheating the tail gas and then sending the tail gas out of a boundary area of the separation system. Liquid at the bottom of the gas-liquid separation tanks at all levels returns to the cold box system by utilizing the pressure of the liquid, is reheated and gathered, then enters the liquid product tank, is subsequently pumped into the cold box system for reheating, and then enters the deethanizer to realize the separation of hydrogen/carbon one/carbon two and carbon three. And tail gas at the top of the deethanizer enters a cold box system, is subjected to multi-stage cooling, throttled and depressurized, returns to the cold box system, is reheated to provide cold energy, and is sent out of a battery limit. After flash evaporation gas generated by the liquid product tank is condensed by a falling film heat exchanger, the gas phase enters a re-heating boundary zone of a cold box system, and a condensed liquid phase (mainly carbon III) flows back to the liquid product tank due to self gravity.
The cold box system (plate-fin heat exchanger) is one of key equipment of the separation system, comprises a heat exchange core body, a matched pipeline, an instrument and other components, mainly meets the heat exchange requirement of multiple flows, and has the advantages of compact structure and high heat exchange efficiency. One part of cold energy of the separation system is from throttling evaporation of a mixture of fresh propane raw material feeding and hydrogen-rich gas in a cold box system, the other part of cold energy is provided by an external refrigeration circulating system, in addition, tail gas at the top of the deethanizer is introduced into the cold box system, and low temperature is generated through temperature reduction and throttling, so that cold energy is provided for the separation system. In order to simplify the process and reduce the investment and energy consumption, the external refrigeration cycle system is composed of two relatively independent refrigeration cycle systems of precooling and deep cooling, and the external refrigeration cycle system basically comprises the following components: the refrigeration cycle compressor, the suction tanks at all stages, pipelines and pipe fittings, control instruments, heat exchangers and the like. The pre-cooling refrigeration cycle system can adopt a single component as a refrigerant, and can also adopt a mixed refrigerant containing two or more of ammonia, ethane, ethylene, propane, propylene, butane and pentane. The deep cooling refrigeration cycle system adopts a multi-component mixture as a mixed refrigerant, and the formula of the mixed refrigerant can be as follows: nitrogen, methane, ethane, ethylene, propane, propylene and butane. The precooling refrigeration circulation system mainly takes charge of cold energy supplement when the temperature of the raw material inlet is between-15 ℃ and-65 ℃, and part of cold energy is also used for condensing a mixed refrigerant of the precooling circulation system and providing cold energy for a tower top condenser of the deethanizer and a falling film condenser at the tank top of the liquid product tank; the cryogenic refrigeration circulation system is mainly used for supplementing cold energy when the refrigeration temperature of the precooling tail end is between-95 ℃ and-160 ℃, and can also be used for supplementing cold energy when the temperature of the raw material inlet is between-95 ℃ and-160 ℃. The refrigerant of the refrigeration cycle system absorbs the heat released by cooling the reaction product in the cold box system through heat recovery, then is gasified and returns to the first section of suction tank of the compressor in each refrigeration cycle system, and then is compressed, cooled and throttled to form low-temperature refrigerant which enters the cold box system to provide cold energy, thereby completing the refrigeration cycle.
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
As shown in figure 2, a reaction product gas at the outlet of a propane dehydrogenation reactor enters a plate-fin heat exchanger EX-101 of a separation system after being pretreated by cooling, compressing, purifying, filtering and the like, is cooled and condensed to-10 ℃, then is sent into a gas-liquid separation tank V101, a separated liquid phase enters a carbon three product tank V-105, a gas phase enters the plate-fin heat exchanger EX-102 and is further cooled and condensed to-38 ℃, then enters a gas-liquid separation tank V-102, a separated liquid phase carbon three is mixed with a liquid phase carbon three separated from the next stage, then is reheated in the plate-fin heat exchanger EX-102 and is gathered to a carbon three product tank V-105 by utilizing the self pressure, a gas phase enters the plate-fin heat exchanger EX-103 and is further cooled and condensed and then enters the gas-liquid separation tank V-103, a separated liquid phase carbon three is mixed with a liquid phase carbon three separated from the next stage and reheated in the plate-fin heat exchanger EX-104, and then sequentially enters the plate-fin heat exchanger EX-103, the gas-liquid separation tank V-103, the gas-102 and the gas-liquid carbon three are reheated in turn, Reheating in the plate-fin heat exchanger EX-102, collecting the gas phase in a carbon three-product tank V-105 by utilizing the self pressure, cooling the gas phase in the plate-fin heat exchanger EX-104 to-115 ℃, and then feeding the gas phase in a gas-liquid separation tank V-104. Obtaining dry gas and circulating gas at the top of a final-stage gas-liquid separation tank V-104, wherein the dry gas returns to plate-fin heat exchange EX-104, EX103, EX-102 and EX-101 in sequence, and is reheated to 30 ℃ and then sent out of a battery limit; circulating gas and fresh propane feed are mixed at the inlet of each stage of plate-fin heat exchanger along the direction of circulating gas input into the cold box system, and then are reheated to 30 ℃ by plate-fin heat exchangers EX-104, EX-103, EX-102 and EX-101, and then are sent out of a battery limit. The tail gas at the top of the deethanizer is cooled to minus 115 ℃ in a multi-stage mode through a cold box system, throttled to 255KPaG, returned to the cold box system, reheated to 25 ℃ and then sent out of the cold box system.
In this example, the reaction product gas was subjected to a total of four gas-liquid separations, and the recycle gas was also subjected to four mixing with the raw material propane. The flow distribution ratio of the propane at the mixing part is about: 7:2:0.7:0.3, with 90% of the fresh propane flow being allocated to the pre-cooling section. Liquid phase products obtained by separation of each stage of gas-liquid separation tank are converged to a carbon three product tank V-105, flash vapor at the tank top of the carbon three product tank V-105 is condensed by a falling film condenser E-201, the uncondensed flash vapor is sent out of a boundary area after being reheated by plate-fin heat exchange EX-102 and EX-101 in sequence, the condensed liquid reflows to the carbon three product tank V-105 due to self gravity, and is finally pressurized to 35 ℃ by a carbon three product pump P-101A/B and sent to a deethanizer for separation of hydrogen/carbon one/carbon two and carbon three.
The cold quantity required to be provided outside the separation system is obtained by two refrigeration circulation systems of propylene precooling and mixed refrigerant copious cooling. The propylene precooling refrigeration cycle system can provide propylene refrigerants at the temperature of-41 ℃ and-15 ℃, wherein the propylene refrigerant at the temperature of-15 ℃ is used by a deethanizer condenser, and the propylene refrigerant at the temperature of-41 ℃ is used by a plate-fin heat exchanger EX-102 and a falling film condenser E-201 at the top of a carbon three product tank V-105. The propylene refrigeration compressor adopts a centrifugal type, the outlet pressure is 1.77MPaG, and the outlet gas phase propylene is cooled to 43 ℃ by circulating cooling water.
The mixed refrigerant cryogenic refrigeration cycle system adopts methane, ethylene and propane as refrigerants, the mixed refrigerant is pressurized to 2.19MPaG by a mixed refrigerant compressor, then is cooled to 43 ℃ by cooling circulating water, sequentially enters the plate-fin heat exchangers EX-101 and EX-102 for precooling to-38 ℃, and then enters the gas-liquid separation tank V-201. And the gas-phase refrigerant on the top of the tank sequentially enters the plate-fin heat exchanger EX-103 and the plate-fin heat exchanger EX-104 to be cooled to the final-stage separation temperature, then is throttled to 320KPaG, then enters the plate-fin heat exchanger EX-104 for reheating, is mixed with the liquid-phase refrigerant at the bottom of the tank cooled by the plate-fin heat exchanger EX-103, enters the plate-fin heat exchanger EX-103 for reheating to-40 ℃, then enters the mixed refrigerant refrigeration compressor to be sucked into the tank, is compressed to the outlet pressure, and completes the refrigeration cycle.
Example 2
As shown in figure 3, the reaction product gas at the outlet of the propane dehydrogenation reactor enters a plate-fin heat exchanger EX-101 of a separation system after being pretreated by cooling, compressing, purifying, filtering and the like, is cooled and condensed to-8 ℃, then is sent into a gas-liquid separation tank V101, the separated liquid phase enters a carbon three product tank V-105, the gas phase enters the plate-fin heat exchanger EX-102 and is further cooled and condensed to-37 ℃, then enters a gas-liquid separation tank V-102, the separated liquid phase carbon three is mixed with the liquid phase carbon three separated from the next stage, is reheated in the EX-102 and is gathered to a carbon three product tank V-105 by utilizing the self pressure, the gas phase enters the plate-fin heat exchanger EX-103 for further cooling and condensation and then enters the gas-liquid separation tank V-103, the separated liquid phase carbon three is mixed with the liquid phase carbon three separated from the next stage and reheated in the plate-fin heat exchanger EX-104, and then sequentially enters the plate-fin heat exchanger EX-103, the gas-liquid carbon three, Reheating in the plate-fin heat exchanger EX-102, collecting the gas phase in a carbon three-product tank V-105 by utilizing the self pressure, cooling the gas phase in the plate-fin heat exchanger EX-104 to-122 ℃, and then feeding the gas phase in a gas-liquid separation tank V-104. Obtaining dry gas at the top of a last-stage gas-liquid separation tank V-104, sequentially returning to plate-fin heat exchange EX-104, EX103, EX-102 and EX-101, reheating to 15 ℃, and then sending out of a battery limit; because the preset hydrogen/hydrocarbon ratio is zero, 80% of fresh propane feed is extracted after precooling to-8 ℃ by EX-101 and then mixed with propane which is cooled to-37 ℃ by EX-102 and then returned to EX-102 for reheating, and the mixture is sent out of a battery limit after reheating to 33 ℃ by EX-101, wherein 100% of the flow of the fresh propane is distributed to a precooling section. The tail gas at the top of the deethanizer is cooled to-122 ℃ in a multi-stage mode through a cold box system, throttled to 285KPaG, returned to the cold box system, reheated to 33 ℃ and sent out of the cold box system.
In the embodiment, the reaction product gas undergoes four gas-liquid separations in total, the fourth-stage separation tank does not generate the circulating gas because the preset hydrogen/hydrocarbon ratio is zero, and the raw material propane is vaporized and gasified in two stages only in the pre-cooling section. The flow distribution ratio of the propane at two positions is about from high to low in the order of temperature: 8:2. Liquid phase products obtained by separation of each stage of gas-liquid separation tank are converged to a carbon three product tank V-105, flash vapor at the tank top of the carbon three product tank V-105 is condensed by a falling film condenser E-201, the uncondensed flash vapor is sent out of a boundary area after being reheated by plate-fin heat exchange EX-102 and EX-101 in sequence, the condensed liquid reflows to the carbon three product tank V-105 due to self gravity, and is finally pressurized to 33 ℃ by a carbon three product pump P-101A/B and sent to a deethanizer for separation of hydrogen/carbon one/carbon two and carbon three.
The cold quantity required to be provided outside the separation system is obtained by two refrigeration circulation systems of propylene precooling and mixed refrigerant copious cooling. The propylene precooling refrigeration cycle system can provide propylene refrigerants at the temperature of-41 ℃ and-15 ℃, wherein the propylene refrigerant at the temperature of-15 ℃ is used by a deethanizer condenser, and the propylene refrigerant at the temperature of-41 ℃ is used by a plate-fin heat exchanger EX-102 and a falling film condenser E-201 at the top of a carbon three product tank V-105. The propylene refrigeration compressor adopts a centrifugal type, the outlet pressure is 1.65MPaG, and the outlet gas phase propylene is cooled to 40 ℃ by circulating cooling water.
The mixed refrigerant cryogenic refrigeration cycle system adopts nitrogen, ethylene and propylene as refrigerants, the mixed refrigerant is pressurized to 2.21MPaG by a mixed refrigerant compressor, then is cooled to 40 ℃ by cooling circulating water, sequentially enters a plate-fin heat exchanger EX-101 and EX-102 for precooling to-37 ℃, and then enters a gas-liquid separation tank V-201. And the gas-phase refrigerant on the top of the tank sequentially enters the plate-fin heat exchanger EX-103 and the plate-fin heat exchanger EX-104 to be cooled to the final-stage separation temperature, then is throttled to 345KPaG, then enters the plate-fin heat exchanger EX-104 for reheating, is mixed with the liquid-phase refrigerant at the bottom of the tank cooled by the plate-fin heat exchanger EX-103, enters the plate-fin heat exchanger EX-103 for reheating to-41 ℃, then enters the mixed refrigerant refrigeration compressor to be sucked into the tank, is compressed to the outlet pressure, and completes the refrigeration cycle.
Example 3
As shown in fig. 4, a reaction product gas at the outlet of a propane dehydrogenation reactor enters a plate-fin heat exchanger EX-101 of a separation system after being pretreated by cooling, compressing, purifying, filtering and the like, is cooled and condensed to-15 ℃, then is sent into a gas-liquid separation tank V101, a separated liquid phase enters a carbon three product tank V-105, a gas phase enters the plate-fin heat exchanger EX-102 and is further cooled and condensed to-30 ℃, then enters a gas-liquid separation tank V102, the separated liquid phase carbon three is mixed with carbon three which is separated at the next stage and is reheated in the plate-fin heat exchanger EX-103, is reheated in the plate-fin heat exchanger EX-102 and is gathered to the carbon three product tank V-105 by utilizing the self pressure, the gas phase enters the plate-fin heat exchanger EX-103, and is cooled to-130 ℃ and then enters the gas-liquid separation tank V-103. Obtaining dry gas and circulating gas at the top of a last-stage gas-liquid separation tank V-103, wherein the dry gas returns to the plate-fin heat exchange EX-103, EX-102 and EX-101 in sequence, and is sent out of a boundary zone after being reheated to 35 ℃; circulating gas and fresh propane feed are mixed at the inlet of each stage of plate-fin heat exchanger along the direction of circulating gas input into the cold box system, and then are reheated to 40 ℃ by plate-fin heat exchangers EX-103, EX-102 and EX-101, and then are delivered out of the boundary zone. And the tail gas at the top of the deethanizer is subjected to multistage cooling to-130 ℃ through a cold box system, throttled to 300KPaG, returned to the cold box system, reheated to 40 ℃ and sent out of the cold box system.
In the present example, the reactants were subjected to a total of three gas-liquid separations, and the recycle gas was also subjected to a total of three mixing with the raw material propane. The flow distribution ratio of the propane at the mixing part is about: 6.5:2:1.5, with 85% of the fresh propane flow being allocated to the pre-cooling section. Liquid phase products obtained by separation of each stage of gas-liquid separation tank are converged to a carbon three product tank V-105, flash vapor at the tank top of the carbon three product tank V-105 is condensed by a falling film condenser E-201, the uncondensed flash vapor is sent out of a boundary area after being reheated by plate-fin heat exchange EX-102 and EX-101 in sequence, the condensed liquid reflows to the carbon three product tank V-105 due to self gravity, and is finally pressurized to 36 ℃ by a carbon three product pump P-101A/B and sent to a deethanizer for separation of hydrogen/carbon one/carbon two and carbon three.
The cold energy required to be provided outside the separation system is obtained by two refrigeration circulation systems of ammonia precooling and mixed refrigerant copious cooling. The ammonia precooling refrigeration cycle system can provide cold energy at the temperature of-33 ℃ and at the temperature of-15 ℃, wherein the cold energy at the temperature of-15 ℃ is used by a condenser of the deethanizer, and the cold energy at the temperature of-33 ℃ is used by a plate-fin heat exchanger EX-102 and a falling film condenser E-201 at the top of a V-105 tank. The ammonia refrigeration compressor adopts a centrifugal type, the outlet pressure is 1.54MPaG, and the outlet gas-phase ammonia is cooled to 40 ℃ by circulating cooling water.
The mixed refrigerant deep cooling refrigeration cycle system adopts nitrogen, ethane and propylene as refrigerants, after the mixed refrigerant is pressurized to 2.08MPaG by a mixed refrigerant compressor, the mixed refrigerant enters a plate-fin heat exchanger EX-101, EX-102 and EX-103 in sequence to be cooled to 40 ℃ through cooling circulating water, the mixed refrigerant enters a plate-fin heat exchanger EX-101, EX-102 and EX-103 to be precooled to the final stage separation temperature, throttling is performed to 285KPaG, the mixed refrigerant enters a plate-fin heat exchanger EX-103 to be reheated to-38 ℃, the mixed refrigerant enters a mixed refrigerant refrigeration compressor suction tank, and the mixed refrigerant is compressed to outlet pressure, so that the refrigeration cycle is completed.
Example 4
The process of this example is the same as example 1, as shown in fig. 5, except that:
the flow distribution ratio of the propane at four positions in sequence from high temperature to low temperature is as follows: 6:2.5:1:0.5, with 85% of the fresh propane flow being allocated to the pre-cooling section. The gas phase in the separation system enters a plate-fin heat exchanger EX-104 to be cooled to-138 ℃ and then enters a gas-liquid separation tank V-104. The tail gas at the top of the deethanizer is cooled to-138 ℃ in a multi-stage mode through a cold box system, throttled to 225KPaG, returned to the cold box system, reheated to 20 ℃ and then sent out of the cold box system. The precooling refrigeration cycle system adopts a mixed refrigerant of propane and propylene and provides refrigeration capacity of two temperature levels of-40 ℃ and-15 ℃ at the same time. The mixed refrigerant of the cryogenic refrigeration circulating system adopts nitrogen, methane, ethane, propane and butane as refrigerants, is pressurized to 2.11MPaG by a cryogenic mixed refrigerant compressor, is cooled to 42 ℃ by circulating cooling water, sequentially enters the plate-fin heat exchangers EX-101 and EX-102 to be precooled to-37 ℃, and then enters the gas-liquid separation tank V-201. Gas-phase cryogen at the top of the tank sequentially enters a plate-fin heat exchanger EX-103 and an EX-104 to be cooled to-138 ℃, then is throttled to 285KPaG, then enters the plate-fin heat exchanger EX-104 to be reheated, is mixed with liquid-phase cryogen at the bottom of the tank cooled by the plate-fin heat exchanger EX-103, then sequentially enters a mixed cryogen refrigeration compressor to be sucked into the tank after being reheated to 25 ℃ by the plate-fin heat exchanger EX-103, the EX-102 and the EX-101, and is compressed to outlet pressure, and refrigeration cycle is completed.
The embodiment can effectively reduce the requirements on the materials of the inlet pipeline of the mixed refrigerant compressor and the compressor body by reheating the mixed refrigerant to the normal temperature, and has the advantages of saving equipment investment and improving the operation stability of the mixed refrigerant compressor. The energy consumption of the precooling refrigeration cycle compressor can also be reduced compared to the specific examples 1 and 2.
Example 5
Example 5 as shown in fig. 6, the flow scheme is substantially identical to that of example 4, with the main differences:
the flow distribution ratio of the propane at four positions in sequence from high temperature to low temperature is as follows: 3.2:2.8:2.2:1.8, wherein 60% of the fresh propane flow is allocated to the pre-cooling section. The gas phase in the separation system enters a plate-fin heat exchanger EX-104 to be cooled to-148 ℃ and then enters a gas-liquid separation tank V-104. The tail gas at the top of the deethanizer is cooled to minus 148 ℃ in a multi-stage mode through a cold box system, throttled to 310KPaG, returned to the cold box system, reheated to 35 ℃ and then sent out of the cold box system. The precooling refrigeration cycle system adopts a mixed refrigerant of ethylene, propylene and pentane. And (3) cooling the water cooler at the outlet of the precooling mixing compressor to 45 ℃, then sequentially entering a plate-fin heat exchanger EX-101 and EX-102 for condensation and cooling to-55 ℃, throttling and reducing the pressure to 175kPaG, returning to the plate-fin heat exchanger EX-102 and EX-101, reheating to the normal temperature, entering a first-section suction tank of the precooling mixing compressor, and then performing two-stage compression to 2.15MPaG to complete the refrigeration cycle.
The cryogenic refrigeration cycle system adopts methane, ethylene and propylene as refrigerants, a cryogenic mixed refrigerant compressor pressurizes the mixture to 2.38MPaG, then the mixture is cooled to 45 ℃ through cooling circulating water, and then the mixture sequentially enters a plate-fin heat exchanger EX-101 and EX-102 to be precooled to-55 ℃ and then enters a gas-liquid separation tank V-201. Gas-phase refrigerant at the top of the tank sequentially enters a plate-fin heat exchanger EX-103 and an EX-104 to be cooled to-148 ℃, is throttled to 335KPaG, then enters the plate-fin heat exchanger EX-104 to be reheated, is mixed with liquid-phase refrigerant at the bottom of the tank cooled by the plate-fin heat exchanger EX-103, then sequentially passes through the plate-fin heat exchanger EX-103, the EX-102 and the EX-101 to be reheated to 27 ℃, enters a mixed refrigerant refrigeration compressor to be sucked into the tank, is compressed to outlet pressure, and completes refrigeration cycle.
The pre-cooling circulation system of the embodiment adopts the mixed refrigerant, and the irreversibility and the temperature difference in the pre-cooling heat transfer process can be reduced by reducing the temperature difference in the pre-cooling heat transfer process
Figure BDA0002807074630000121
Loss is reduced, energy consumption of the precooling circulating compressor is reduced, and the gain effect of reducing energy consumption of the whole separation device is achieved.
Meanwhile, the specific embodiment adopts the dual-cycle mixed refrigerant for refrigeration, and the power consumption of the two mixed refrigerant compressors is consistent by adjusting the formulas of the two sets of mixed refrigerants, so that the two mixed refrigerant compressors can be matched with power devices with the same specification, and the gain effect of reducing the set difficulty and the operation difficulty of the compressor unit is achieved.
Comparative example 1
The separation apparatus was constructed in accordance with example 1 using the separation flow and apparatus for the product of propane dehydrogenation reaction shown in FIG. 7.
The process flow parameters of comparative example 1 and example 1 also remained the same, with the main differences: 1. comparative example 1 does not adopt the design of mixing, throttling and evaporating fresh raw material propane and circulating gas at multiple positions; 2. comparative example 1 no design was used to cool the tail gas from the top of the deethanizer and reheat it to provide cold to the separation system.
The shaft powers of the two refrigeration compressors of example 1 and comparative example 1 were compared as follows:
unit of Comparative example 1 Example 1
Precooling circulating compressor shaft power kW 9235 2455
Shaft power of cryogenic circulating compressor kW 2471 1765
Total load of refrigeration cycle cooler MW 28.95 10.43
It can be seen from comparison that, in comparative example 1, because the refrigeration quantities of the raw material propane and the tail gas at the top of the deethanizer are not coupled into the separation system, the shaft powers of the two external refrigeration compressors are both greater than those in example 1, and the total load of the refrigeration cycle cooler is also much greater than that in example 1, which shows that example 1 has great advantage in saving the energy consumption of the separation system.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims (10)

1. A method for separating a coupling type alkane catalytic dehydrogenation reaction product is characterized by comprising the following steps:
inputting reaction product gas at the outlet of the alkane catalytic dehydrogenation reactor into a cold box system to obtain a cooled product;
inputting the cooled product into N-stage gas-liquid separation tanks connected in series for gas-liquid separation, and then:
re-inputting the gas-phase products obtained from the 1 st to the N-1 st level into the cold box system;
the liquid phase products obtained from the 1-N stages are collected and then reheated and sent out of a cold box system, and then the separation of the products with different carbon numbers of the liquid phase products is realized through a separation tower;
mixing the circulating gas obtained from the top of the Nth-stage gas-liquid separation tank with fresh propane according to a preset hydrogen/hydrocarbon ratio by M stages, throttling and evaporating in a cold box system, providing cold energy for the cold box system, reheating and then sending out the cold box system, wherein M is less than or equal to N;
introducing tail gas at the top of the deethanizer into a cold box system, providing cold energy for the cold box system, and sending the cold box system out after reheating;
the cold energy of the cold box system is also from an external refrigeration cycle system.
2. The method for separating the coupled alkane catalytic dehydrogenation reaction product according to claim 1, wherein the number of series stages of the heat exchanger in the cold box system is equal to and matched with that of the N-stage separation tank, the cold box system comprises one or more stages thereof to form a pre-cooling section, and the rest of the cold box system forms a deep cooling section.
3. The method as claimed in claim 2, wherein 60-100% of the fresh propane flow is distributed to the pre-cooling section, and the rest is distributed to the deep cooling section, and the distributed flow is matched with the fresh propane temperature according to negative correlation.
4. The method of claim 2, wherein the external refrigeration cycle system comprises: a precooling refrigeration circulation system for providing cold energy to the precooling section and a deep cooling refrigeration circulation system for providing cold energy to the deep cooling section.
5. The method as claimed in claim 4, wherein the refrigerant in the pre-cooling refrigeration cycle system is one or more of ammonia, ethane, ethylene, propylene, propane, butane and pentane;
the refrigerant in the cryogenic refrigeration cycle system is a combination of a plurality of nitrogen, methane, ethane, ethylene, propane, propylene and butane.
6. The method of claim 1, wherein the recycle gas flow rate is matched in proportion to a predetermined hydrogen/hydrocarbon ratio;
when the preset hydrogen/hydrocarbon ratio is zero, the circulating gas flow is set to be zero, and the fresh propane is throttled and evaporated only in the corresponding stage of the pre-cooling section.
7. The method for separating the product of the coupled catalytic dehydrogenation of alkane according to claim 1, wherein the tail gas from the top of the deethanizer is cooled to the temperature for the nth stage separation by a cooling box system, throttled back to the cooling box system, and reheated and sent out of the cooling box system.
8. An apparatus for separating a product of a coupled alkane catalytic dehydrogenation reaction, comprising:
the cold box system is respectively connected with an outlet of the alkane catalytic dehydrogenation reactor and a tail gas outlet at the top of the separation tower and is connected with a fresh propane storage tank, and the cold box system comprises a pre-cooling section and a deep cooling section;
the precooling refrigeration circulation system is connected with the precooling section in a heat exchange manner and provides cold energy for the precooling, cooling and separating process of the reaction product gas at the outlet of the alkane catalytic dehydrogenation reactor;
the cryogenic refrigeration circulating system is connected with the cryogenic section in a heat exchange manner and provides cold energy for the cryogenic cooling separation process of the reaction product gas at the outlet of the alkane catalytic dehydrogenation reactor;
and the N-stage separation tank is connected with the cold box system and is matched with the cold box system step by step, the circulating gas obtained from the top of the Nth-stage separation tank and the fresh propane are mixed by M stages according to a preset hydrogen/hydrocarbon ratio and are input into the cold box system, wherein M is less than or equal to N, and outlets of liquid-phase products obtained from 1-N stages of the separation tank are sequentially connected with the liquid product tank and the separation tower, so that the separation of the products with different carbon numbers is realized.
9. The apparatus of claim 8, wherein the liquid product tank is further provided with a falling film condenser at the top;
the separation tower is a deethanizer;
the cold box system comprises a multi-stage plate-fin heat exchanger.
10. The apparatus of claim 9, wherein the pre-cooling refrigeration cycle system is further connected to the condenser of the deethanizer, the falling-film condenser, and the cryogenic refrigeration cycle system in a heat-exchanging manner.
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