Ethylene cracking furnace system, cracking method

Abstract

The present application relates to the technical field of ethylene cracking, in particular to an ethylene cracking furnace system and a cracking method. The ethylene cracking furnace system provided by the present application limits the structure of the burner in the ethylene cracking furnace, so that the staged combustion of the oxygen-rich gas and the natural gas is fully carried out, the appearance of the local high-temperature area in the furnace is avoided, the CO2 concentration in the high-temperature flue gas is improved, the CO2 capture rate is effectively improved, and the capture cost is reduced. In combination with the CO2 recovery device, the CO2 in the high-temperature flue gas is recovered, and the CO2-rich stream is obtained.

Description

Technical Field

[0001] This invention relates to the field of ethylene cracking technology, specifically to an ethylene cracking furnace system and a cracking method. Background Technology

[0002] The ethylene industry is the leading sector of the petrochemical industry, and ethylene cracking furnaces are the main production units for organic chemical raw materials. The heat required for cracking furnaces is obtained through the combustion of fuel in burners located in the radiant section of the furnace. Currently, natural gas and air are used as the combustion medium. However, the large amount of nitrogen present in the air is detrimental to the combustion process: firstly, nitrogen's diatomic symmetry structure prevents it from emitting or absorbing radiation, weakening heat transfer within the furnace; secondly, the high-temperature nitrogen produced during combustion is ultimately discharged with the flue gas, resulting in significant heat loss. Simultaneously, the combustion process generates large amounts of carbon dioxide, exacerbating the greenhouse effect and contradicting the current development goals of achieving carbon peaking and carbon neutrality. Therefore, the greening of cracking furnaces has always been a key research focus in the cracking field.

[0003] Carbon dioxide is widely present in the atmosphere and dissolved in water. At room temperature, carbon dioxide is a colorless and odorless gas, a relatively inert molecule, and chemically stable. Carbon dioxide is a major contributor to the greenhouse effect and is also a very valuable resource with high civilian and industrial value. In my country, the carbon dioxide needed for industry is mostly obtained through methods such as calcining limestone and utilizing waste gas from chemical and brewing industries, but these methods are energy-intensive. In contrast, the main component of the flue gas emitted from air combustion is NO. X The carbon dioxide concentration is low, making its capture difficult and resulting in high energy consumption and recycling costs.

[0004] When the oxygen concentration in the combustion air reaches 90%-100%, this combustion state is called pure oxygen combustion. Using pure oxygen for combustion directly avoids the large amounts of nitrogen in conventional combustion air entering the pyrolysis furnace, thus blocking the nitrogen source and effectively reducing NO. X While increasing combustion volume, it can reduce smoke loss and effectively improve combustion efficiency. Furthermore, by using pure oxygen for combustion, the combustion reaction will be more complete, significantly increasing the carbon dioxide content in the flue gas and reducing the difficulty of carbon dioxide capture and treatment. This is a superior energy-saving comprehensive technology compared to air-assisted combustion.

[0005] CN205328948U discloses a burner arrangement structure for an ethylene cracking furnace, specifically including: bottom burners arranged at the bottom of the cracking furnace, and sidewall burners arranged in a single row in the middle of the sidewalls of the cracking furnace. Both the bottom burners and the sidewall burners can form a long, vertically upward flame. This burner arrangement structure for an ethylene cracking furnace can effectively reduce the number of sidewall burners, thereby reducing construction and maintenance costs, while simultaneously meeting the requirements for cracking furnace combustion capacity, flame shape, and NO₂.X Requirements for emissions and heat flux density distribution. However, it still uses an air-assisted combustion method and does not consider the issue of carbon dioxide emissions in the flue gas.

[0006] Therefore, a new ethylene cracking furnace system is urgently needed. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of large CO2 emissions, high flue gas loss, and low energy utilization in existing ethylene cracking furnaces that use air-assisted combustion. This invention provides an ethylene cracking furnace system and a cracking method thereof. The system reduces CO2 emissions, minimizes flue gas loss, and achieves high thermal efficiency. At the same time, it recovers and utilizes CO2 from high-temperature flue gas, reducing the difficulty and cost of CO2 capture and improving resource utilization.

[0008] To achieve the above objectives, a first aspect of the present invention provides an ethylene cracking furnace system, comprising: an ethylene cracking furnace and a CO2 recovery device connected in sequence; the ethylene cracking furnace comprising: a convection section having a lower opening and a radiation section having an upper opening, wherein the convection section and the radiation section are connected through the lower opening and the upper opening; the radiation section comprising: a cracking furnace tube, a cracking furnace chamber, and at least one burner; each burner is independently provided with an oxygen-enriched gas nozzle, a primary natural gas passage, and at least one secondary natural gas passage;

[0009] The pyrolysis furnace is used to stage the combustion of oxygen-enriched gas and natural gas. The staged combustion products transfer heat to the pyrolysis furnace tubes, and the heat-exchanged products enter the convection section.

[0010] The convection section is used to exchange heat between the heat-exchanged product and the pyrolysis feedstock to obtain high-temperature flue gas converted from the heat-exchanged product and heated pyrolysis feedstock converted from the pyrolysis feedstock.

[0011] The CO2 recovery device is used to cool and recover CO2 from the high-temperature flue gas to obtain a CO2-rich stream.

[0012] A second aspect of the present invention provides a pyrolysis method, which is performed in the system provided in the first aspect.

[0013] Preferably, the method includes the following steps:

[0014] (1) The oxygen-enriched gas and natural gas are staged in the pyrolysis furnace, and the staged combustion products are transferred to the pyrolysis furnace tubes to obtain the heat exchanged products.

[0015] (2) The heat-exchange product is introduced into the convection section and the pyrolysis feedstock for heat exchange to obtain high-temperature flue gas transformed from the heat-exchange product and heated pyrolysis feedstock transformed from the pyrolysis feedstock.

[0016] (3) The high-temperature flue gas is cooled and recovered in the CO2 recovery device of the system to obtain a CO2-rich stream.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The ethylene cracking furnace system provided by this invention, by defining the structure of the burners in the ethylene cracking furnace, namely, each burner is independently equipped with an oxygen-enriched gas nozzle, a primary natural gas channel and at least one secondary natural gas channel, so that the staged combustion of oxygen-enriched gas and natural gas can be fully carried out, avoiding the occurrence of local high-temperature areas in the furnace, increasing the CO2 concentration in the high-temperature flue gas, effectively improving the CO2 capture rate and reducing the capture cost; and combined with a CO2 recovery device, CO2 in the high-temperature flue gas is recovered to obtain a CO2-rich stream.

[0019] Specifically, compared to air combustion, oxygen-enriched gas combustion has increased gas radiation capacity, and the combustion products are mainly carbon dioxide and water vapor. As asymmetric gas molecules, they have strong radiation capacity, which is beneficial to improving the heat transfer effect in the pyrolysis furnace. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of an ethylene cracking furnace system provided by the present invention;

[0021] Figure 2 This is a top view schematic diagram of a burner provided by the present invention;

[0022] Figure 3 This is a top view schematic diagram of another burner provided by the present invention.

[0023] Explanation of reference numerals in the attached figures

[0024] I. Ethylene Cracking Furnace II. CO2 Recovery Unit III. Oxygen Supply Unit

[0025] II-1, First heat exchanger; II-2, Second heat exchanger; II-3, Compressor

[0026] 1. Convection section; 2. Radiation section; 3. Bottom burner

[0027] 4. Side burner; 5. Cracking furnace tube; 6. Oxygen-enriched gas

[0028] 7. Natural gas 8. Quenching boiler 9. Cracking feedstock inlet

[0029] 10. High-temperature flue gas outlet; 11. Cooling water; 12. Low-temperature flue gas.

[0030] 13. CO2-rich logistics; 14. Exhaust gas; 15. Oxygen-rich gas nozzle.

[0031] 16. Primary natural gas channel; 17. Secondary natural gas channel; 18. Nozzle. Detailed Implementation

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] In this invention, unless otherwise specified, the top refers to the position of 0-10% of the reactor from top to bottom; the upper part refers to the position of 10-30% of the reactor from top to bottom; the middle part refers to the position of 30-70% of the reactor from top to bottom; the lower part refers to the position of 70-90% of the reactor from top to bottom; and the bottom refers to the position of 90-100% of the reactor from top to bottom.

[0034] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish between them. For example, in "first heat exchange" and "second heat exchange," "first" and "second" are simply used to distinguish that they are not the same heat exchange.

[0035] The first aspect of the present invention provides an ethylene cracking furnace system, the system comprising: an ethylene cracking furnace and a CO2 recovery device connected in sequence; the ethylene cracking furnace comprising: a convection section having a lower opening and a radiation section having an upper opening, wherein the convection section and the radiation section are connected through the lower opening and the upper opening; the radiation section comprising: a cracking furnace tube, a cracking furnace chamber and at least one burner; each burner is independently provided with an oxygen-enriched gas nozzle, a primary natural gas passage and at least one secondary natural gas passage;

[0036] The pyrolysis furnace is used to stage the combustion of oxygen-enriched gas and natural gas. The staged combustion products transfer heat to the pyrolysis furnace tubes, and the heat-exchanged products enter the convection section.

[0037] The convection section is used to exchange heat between the heat-exchanged product and the pyrolysis feedstock to obtain high-temperature flue gas converted from the heat-exchanged product and heated pyrolysis feedstock converted from the pyrolysis feedstock.

[0038] The CO2 recovery device is used to cool and recover CO2 from the high-temperature flue gas to obtain a CO2-rich stream.

[0039] The inventors of this invention discovered that when oxygen-enriched gas and natural gas are fully combusted in the pyrolysis furnace, carbon dioxide and water are produced. The heat generated by combustion ensures the smooth progress of the pyrolysis reaction within the furnace tubes. Subsequently, the combustion products enter the convection section through the transverse section of the pyrolysis furnace, preheating the pyrolysis feedstock to the temperature required for the pyrolysis reaction. After heat exchange, the products are discharged through the convection section and enter the subsequent CO2 recovery unit. Using oxygen-enriched gas combustion reduces the proportion of nitrogen (which has no thermal radiation capacity), enhancing heat transfer between the flue gas in the radiant section and the pyrolysis furnace tubes. Furthermore, it increases the CO2 concentration in the flue gas, reducing the difficulty of CO2 capture and collection.

[0040] Compared with the prior art, the present invention adopts oxygen-enriched gas combustion, which has the following advantages: (1) Since radiation heat transfer is the main way of heat transfer in pyrolysis furnace, according to the characteristics of gas radiation, only triatomic gas and polyatomic gas have radiation ability, while diatomic gas has almost no radiation ability. In the case of conventional air-assisted combustion, the proportion of nitrogen gas with no radiation ability is very high, and the smoke opacity is very low, which affects the radiation heat transfer process of smoke gas to furnace tubes. With oxygen-enriched gas combustion, due to the low nitrogen content, the amount of combustion gas and smoke gas are significantly reduced. Therefore, the flame temperature and opacity increase with the increase of the oxygen ratio in the combustion gas. (2) By using oxygen-enriched gas to assist combustion, the flame becomes shorter, the combustion intensity increases, and the combustion speed increases. This will help the combustion reaction to proceed completely, improve the fuel utilization efficiency, and thus improve the thermal efficiency of the pyrolysis furnace. At the same time, it also increases the CO2 content in the flue gas, reducing the difficulty and cost of CO2 capture. (3) By using oxygen-enriched gas to assist combustion, the excess air coefficient can be appropriately reduced, the exhaust volume and the amount of flue gas after combustion can be reduced, thereby reducing exhaust losses and ensuring the energy-saving, green and efficient operation of the pyrolysis furnace.

[0041] Meanwhile, in order to avoid the combustion reaction being concentrated near the burner outlet, a staged combustion method is adopted for heating, that is, each burner is equipped with an oxygen-enriched gas nozzle, a primary natural gas passage and at least one secondary natural gas passage.

[0042] According to the present invention, preferably, the pyrolysis furnace tube is disposed inside the pyrolysis furnace chamber for pyrolysis reaction of the heated pyrolysis feedstock.

[0043] According to the present invention, preferably, the mass flow ratio of the oxygen-enriched gas and the natural gas is 0.1-0.5:1, for example, 0.1:1, 0.3:1, 0.35:1, 0.4:1, 0.5:1, and any value within the range of any two values, preferably 0.3-0.4:1.

[0044] According to the present invention, preferably, the oxygen content in the oxygen-enriched gas is 70-100% by volume, more preferably 90-100% by volume; the oxygen excess coefficient is 1-1.5, more preferably 1.1-1.2.

[0045] According to the present invention, preferably, the pyrolysis feedstock is selected from at least one of ethane, naphtha, hydrotreated tail oil and diesel.

[0046] According to the present invention, preferably, the convection section is provided with a pyrolysis feedstock inlet and a high-temperature flue gas outlet.

[0047] According to the present invention, preferably, the burner includes a bottom burner and a sidewall burner, which are respectively disposed at the bottom and sidewall of the radiant section; more preferably, the ratio of the number of bottom burners to sidewall burners is 1:1.5-3, for example, 1:1.5, 1:2, 1:2.25, 1:2.5, 1:3, and any value in any range of any two values, preferably 1:2-2.5.

[0048] According to the present invention, preferably, the number of bottom burners is ≥2, and more preferably 2-8.

[0049] According to the present invention, preferably, the oxygen-enriched gas nozzle is a cylindrical nozzle and is disposed on the central axis of the burner.

[0050] According to the present invention, preferably, the upper part of the oxygen-enriched gas nozzle is provided with at least one spray hole, and the spray holes are preferably arranged on the same axis; more preferably, the number of spray holes is ≥2, and more preferably 3-4.

[0051] According to the present invention, preferably, the angle between the centerline of the nozzle and the horizontal plane is 60-90°, for example, 60°, 70°, 75°, 80°, 90°, and any value within the range of any two values, preferably 70-80°.

[0052] In some embodiments of the present invention, preferably, based on the total volumetric flow rate of the natural gas, the volumetric flow rate ratio of the primary gas passage and the secondary gas passage is 25-45:75-55, more preferably 30-40:70-60.

[0053] According to the present invention, preferably, the cross-sections of the primary natural gas channel and the secondary natural gas channel are each independently selected from circular or rectangular.

[0054] According to the present invention, preferably, the secondary natural gas channel is arranged on both sides of the long side of the primary natural gas channel, and the secondary gas channel is preferably arranged on the same axis, or arranged in a circle around the primary natural gas channel.

[0055] According to the present invention, preferably, the number of secondary natural gas channels is ≥2, and more preferably 4-10.

[0056] A top view schematic diagram of a burner provided by this invention is shown below. Figure 2 As shown, by Figure 2 It is known that the burner is equipped with an oxygen-enriched gas nozzle 15, a primary gas passage 16, and eight secondary gas passages 17. The oxygen-enriched gas nozzle 15 is cylindrical and is located on the central axis of the burner. The upper part of the oxygen-enriched gas nozzle 15 is provided with eight nozzle holes 18, which are arranged in two rows on the axis of the burner. The center line of the nozzle holes 18 makes an angle of 60-90° with the horizontal plane. The primary natural gas passage 16 has a rectangular cross-section, the secondary natural gas passages 17 have rectangular cross-sections, and the eight secondary natural gas passages 17 are arranged in a straight line on both sides of the long side of the primary natural gas passage 16.

[0057] A top view schematic diagram of another burner provided by the present invention is shown below. Figure 3 As shown, by Figure 3 It is known that the burner is equipped with an oxygen-enriched gas nozzle 15, a primary gas passage 16, and eight secondary gas passages 17. The oxygen-enriched gas nozzle 15 is cylindrical and is located on the central axis of the burner. The upper part of the oxygen-enriched gas nozzle 15 is provided with eight nozzle holes 18, which are arranged in two rows on the axis of the burner. The center line of the nozzle holes 18 makes an angle of 60-90° with the horizontal plane. The cross-section of the primary natural gas passage 16 is rectangular, and the cross-section of the secondary natural gas passages 17 is circular. The eight secondary natural gas passages 17 are arranged in a circle around the primary natural gas passage 16.

[0058] According to the present invention, preferably, the CO2 recovery device includes a first heat exchanger and a second heat exchanger connected in sequence.

[0059] According to the invention, preferably, the first heat exchanger is used to perform a first heat exchange between the high-temperature flue gas and the first cooling medium to obtain low-temperature flue gas and cooling water. In this invention, the first heat exchange aims to remove water from the high-temperature flue gas.

[0060] According to the invention, preferably, the second heat exchanger is used to perform a second heat exchange between the low-temperature flue gas and the second cooling medium to obtain a CO2-rich stream and exhaust gas. In this invention, the second heat exchange aims to liquefy the CO2 in the low-temperature flue gas.

[0061] In this invention, the types of the first heat exchanger and the second heat exchanger are not limited, and include, but are not limited to, conventional heat exchanger types in the art.

[0062] According to the present invention, preferably, the first cooling medium and the second cooling medium are each independently selected from ethylene and / or propylene. In the present invention, both the first cooling medium and the second cooling medium are derived from ethylene and propylene from the de-ethanizer and de-propaneizer in the ethylene plant process, eliminating the need for an additional refrigeration system, reducing energy consumption, and achieving resource recycling.

[0063] According to the present invention, preferably, the CO2 recovery device further includes a compressor; more preferably, the compressor is disposed between the first heat exchanger and the second heat exchanger, for compressing the low-temperature flue gas to obtain compressed low-temperature flue gas.

[0064] According to the present invention, preferably, the radiant section further includes a quench boiler connected to the pyrolysis furnace tube; more preferably, the quench boiler is connected to the top of the pyrolysis furnace tube.

[0065] According to the present invention, preferably, the system further includes: an oxygen supply device connected to the oxygen-enriched gas nozzle; more preferably, the oxygen supply device is selected from an air separation unit, a water electrolysis unit, or a liquid oxygen storage tank in an oil refining unit.

[0066] A schematic diagram of an ethylene cracking furnace system provided by this invention is shown below. Figure 1-2 As shown, the system includes: an oxygen supply device III, an ethylene cracking furnace I, and a CO2 recovery device II connected in sequence. The ethylene cracking furnace I includes: a convection section 1 with a lower opening and a radiation section 2 with an upper opening, and the convection section 1 and the radiation section 2 are connected through the lower opening and the upper opening. The radiation section 2 includes: a cracking furnace tube 5, a cracking furnace chamber, a bottom burner 3, a side wall burner 4, and a cracking furnace tube 8. The bottom burner 3 and the side wall burner 4 are each independently equipped with an oxygen-enriched gas nozzle 15, a primary natural gas channel 16, and a secondary natural gas channel 17. The top of the cracking furnace tube 5 is connected to a quench boiler 8. The convection section 1 is equipped with a cracking feedstock inlet 9 and a high-temperature flue gas outlet 10.

[0067] The pyrolysis furnace is used to stage the combustion of oxygen-enriched gas 6 and natural gas 7. The staged combustion products transfer heat to the pyrolysis furnace tube 5, and the heat-exchanged products enter the convection section 1. The convection section 1 is used to exchange heat between the heat-exchanged products and the pyrolysis feedstock to obtain high-temperature flue gas converted from the heat-exchanged products and heated pyrolysis feedstock converted from the pyrolysis feedstock. The high-temperature flue gas enters the CO2 recovery unit II through the high-temperature flue gas outlet 10.

[0068] CO2 recovery device II includes: a first heat exchanger II-1, a compressor II-3, and a second heat exchanger II-2 connected in sequence. The first heat exchanger II-1 is used to perform a first heat exchange between high-temperature flue gas and a first cooling medium to obtain low-temperature flue gas 12 and cooling water 11. The compressor II-3 is used to compress the low-temperature flue gas 12 to obtain compressed low-temperature flue gas. The second heat exchanger II-2 is used to perform a second heat exchange between the compressed low-temperature flue gas and the second cooling medium to obtain CO2-rich stream 13 and waste gas 14.

[0069] According to a particularly preferred embodiment of the present invention, the system includes: an ethylene cracking furnace and a CO2 recovery device connected in sequence; the ethylene cracking furnace includes: a convection section having a lower opening and a radiation section having an upper opening, and the convection section and the radiation section are connected through the lower opening and the upper opening; the radiation section includes: a cracking furnace tube, a cracking furnace chamber and at least one burner; each burner is independently provided with an oxygen-enriched gas nozzle, a primary natural gas passage and at least one secondary natural gas passage;

[0070] The pyrolysis furnace is used to stage the combustion of oxygen-enriched gas and natural gas. The staged combustion products transfer heat to the pyrolysis furnace tubes, and the heat-exchanged products enter the convection section.

[0071] The convection section is used to exchange heat between the heat-exchanged product and the pyrolysis feedstock to obtain high-temperature flue gas converted from the heat-exchanged product and heated pyrolysis feedstock converted from the pyrolysis feedstock.

[0072] The CO2 recovery device is used to cool and recover CO2 from the high-temperature flue gas to obtain a CO2-rich stream.

[0073] The ratio of bottom burners to sidewall burners is 1:1.5-3;

[0074] Wherein, based on the total volumetric flow rate of the natural gas, the volumetric flow rate ratio of the primary gas passage and the secondary gas passage is 25-45:75-55.

[0075] A second aspect of the present invention provides a pyrolysis method, which is performed in the system provided in the first aspect.

[0076] In some embodiments of the present invention, preferably, the method includes the following steps:

[0077] (1) The oxygen-enriched gas and natural gas are staged in the pyrolysis furnace, and the staged combustion products are transferred to the pyrolysis furnace tubes to obtain the heat exchanged products.

[0078] (2) The heat-exchange product is introduced into the convection section and the pyrolysis feedstock for heat exchange to obtain high-temperature flue gas transformed from the heat-exchange product and heated pyrolysis feedstock transformed from the pyrolysis feedstock.

[0079] (3) The high-temperature flue gas is cooled and recovered in the CO2 recovery device of the system to obtain a CO2-rich stream.

[0080] In some embodiments of the present invention, preferably, the CO2 content in the CO2-rich stream is ≥90% by mass, and more preferably 96-99% by mass.

[0081] In this invention, to improve the thermal efficiency of the ethylene cracking furnace, it is necessary to control the temperature of the high-temperature flue gas discharged from the convection section, i.e., the exhaust gas temperature, which should be as low as possible. However, if the exhaust gas temperature is too low, it may cause low-temperature dew point corrosion, damaging some heat exchange tubes in the convection section. Therefore, the exhaust gas temperature should be appropriate. Preferably, the temperature of the high-temperature flue gas is 120-130°C, for example, 120°C, 125°C, 126°C, 127°C, 128°C, 130°C, or any value within any range of two such values, preferably 125-128°C; more preferably, the CO2 concentration in the high-temperature flue gas is 15-40% by mass, for example, 15% by mass, 20% by mass, 25% by mass, 30% by mass, 40% by mass, or any value within any range of two such values, preferably 20-30% by mass.

[0082] In some embodiments of the present invention, preferably, the heated pyrolysis feedstock is introduced into the pyrolysis furnace tube of the system for pyrolysis reaction.

[0083] According to the present invention, preferably, the cooling and recovery process includes: subjecting the high-temperature flue gas to a first heat exchange and subjecting the resulting low-temperature flue gas to a second heat exchange to obtain the CO2-rich stream.

[0084] In some embodiments of the present invention, preferably, the temperature of the low-temperature flue gas is 0-8°C, more preferably 0-5°C, to remove most of the water in the flue gas, such that the water content in the low-temperature flue gas is ≤10% by volume, preferably 5-7% by volume; after dehydration, the carbon dioxide content in the flue gas is further increased, which is beneficial to achieving CO2 capture.

[0085] In some embodiments of the present invention, preferably, before the second heat exchange, the low-temperature flue gas is compressed so that the pressure of the compressed low-temperature flue gas reaches 1-3 MPa and the temperature drops to -10°C to -5°C, in order to liquefy the CO2 in the low-temperature flue gas and obtain a CO2-rich stream. Under these conditions, the CO2 in the flue gas is liquefied, while the light gases (N2, O2) in the flue gas do not liquefy, thereby achieving the separation of CO2 from other gases in the flue gas.

[0086] The method provided by this invention achieves CO2 separation by condensing and liquefying the gas through pressurization and cooling, thus changing the CO2 from a gaseous state to a liquid state. This facilitates the transportation and storage of CO2 and avoids the use of chemical or physical absorbents, eliminating the problem of absorbent corrosion. While the low-temperature method is suitable for capturing flue gas with high CO2 concentrations, it yields high-concentration CO2. However, the compression and condensation processes are energy-intensive. In this invention, the CO2 recovery device uses cooling media derived from ethylene and propylene from the ethylene de-ethane and de-propane towers in the ethylene process. Therefore, no additional refrigeration system is required, reducing energy consumption and achieving resource recycling.

[0087] The present invention will be described in detail below through embodiments.

[0088] Example 1

[0089] Ethylene cracking furnace system ,like Figure 1-2 As shown, the system includes: an oxygen supply unit III, an ethylene cracking furnace I, and a CO2 recovery unit II connected in sequence. The ethylene cracking furnace I includes: a convection section 1 with a lower opening and a radiation section 2 with an upper opening, and the convection section 1 and the radiation section 2 are connected through the lower opening and the upper opening; the radiation section 2 is provided with a cracking furnace tube 5, a cracking furnace chamber, a bottom burner 3 and a side wall burner 4, and a quench boiler 8 connected to the top of the cracking furnace tube 5; the convection section 1 is provided with a cracking feedstock inlet 9 and a high-temperature flue gas outlet 10; the CO2 recovery unit II includes: a first heat exchanger II-1, a compressor II-3 and a second heat exchanger II-2 connected in sequence; the ratio of the number of bottom burners 3 to side wall burners 4 is 1:2.

[0090] The bottom burner 3 and the side wall burner 4 are each independently equipped with an oxygen-enriched gas nozzle 15, a primary gas passage 16, and a secondary gas passage 17. The oxygen-enriched gas nozzle 15 is cylindrical and is located on the central axis of the burner. The upper part of the oxygen-enriched gas nozzle 15 is provided with eight nozzle holes 18, which are arranged in two rows on the axis of the burner. The center line of the nozzle holes 18 makes an angle of 75° with the horizontal plane. The primary natural gas passage 16 has a rectangular cross-section, and the secondary natural gas passage 17 has a rectangular cross-section. The eight secondary natural gas passages 17 are arranged in a straight line on both sides of the long side of the primary natural gas passage 16.

[0091] Pyrolysis method

[0092] (1) Oxygen-enriched gas (oxygen content of 95% by volume and oxygen excess coefficient of 1.1) and natural gas are staged combustion in the pyrolysis furnace. The staged combustion products are transferred to the pyrolysis furnace tubes to obtain heat exchanged products.

[0093] The mass flow rate ratio of oxygen-enriched gas to natural gas is 0.3:1; based on the total volumetric flow rate of natural gas, the volumetric flow rate ratio of the primary gas passage to the secondary gas passage is 40:60.

[0094] (2) The heat exchanged product is fed into the convection section to preheat the cracking feedstock (ethane) to obtain high-temperature flue gas P1 converted from the heat exchanged product and heated cracking feedstock converted from the cracking feedstock.

[0095] The temperature of the high-temperature flue gas P1 is 125°C, and the CO2 content in the high-temperature flue gas P1 is 30% by mass.

[0096] (3) The high-temperature flue gas is first exchanged with ethylene in the CO2 recovery device of the system to obtain a low-temperature flue gas with a temperature of 6°C. After compression, it is then exchanged with ethylene again to obtain a CO2-rich stream S1.

[0097] In CO2-rich stream S1, the CO2 content is 97% by mass.

[0098] Example 2

[0099] Ethylene cracking furnace system ,like Figure 1 , 3 As shown, the system includes: an oxygen supply unit III, an ethylene cracking furnace I, and a CO2 recovery unit II connected in sequence. The ethylene cracking furnace I includes: a convection section 1 with a lower opening and a radiation section 2 with an upper opening, and the convection section 1 and the radiation section 2 are connected through the lower opening and the upper opening; the radiation section 2 is provided with a cracking furnace tube 5, a cracking furnace chamber, a bottom burner 3 and a side wall burner 4, and a quench boiler 8 connected to the top of the cracking furnace tube 5; the convection section 1 is provided with a cracking feedstock inlet 9 and a high-temperature flue gas outlet 10; the CO2 recovery unit II includes: a first heat exchanger II-1, a compressor II-3 and a second heat exchanger II-2 connected in sequence.

[0100] The bottom burner 3 and the side wall burner 4 are each independently equipped with an oxygen-enriched gas nozzle 15, a primary gas passage 16, and a secondary gas passage 17. The oxygen-enriched gas nozzle 15 is cylindrical and is located on the central axis of the burner. The upper part of the oxygen-enriched gas nozzle 15 is provided with eight nozzle holes 18, which are arranged in two rows on the axis of the burner. The center line of the nozzle holes 18 makes an angle of 90° with the horizontal plane. The cross-section of the primary natural gas passage 16 is rectangular, and the cross-section of the secondary natural gas passage 17 is circular. The eight secondary natural gas passages 17 are arranged in a circle around the primary natural gas passage 16.

[0101] Pyrolysis method

[0102] (1) Oxygen-enriched gas (oxygen content of 98% by volume, oxygen excess coefficient of 1.2) and natural gas are staged combustion in the pyrolysis furnace of the above system. The staged combustion products are transferred to the pyrolysis furnace tubes to obtain heat exchanged products.

[0103] The mass flow rate ratio of oxygen-enriched gas to natural gas is 0.4:1; based on the total volumetric flow rate of natural gas, the volumetric flow rate ratio of the primary gas passage to the secondary gas passage is 30:70.

[0104] (2) The heat exchanged product is fed into the convection section to preheat the cracking feedstock (naphtha) to obtain high-temperature flue gas P2 converted from the heat exchanged product and heated cracking feedstock converted from the cracking feedstock.

[0105] The temperature of the high-temperature flue gas P2 is 128°C, and the CO2 content in the high-temperature flue gas P2 is 40% by mass.

[0106] (3) The high-temperature flue gas is first exchanged with ethylene in the CO2 recovery device of the system to obtain a low-temperature flue gas with a temperature of 5°C. After compression, it is then exchanged with ethylene again to obtain a CO2-rich stream S2.

[0107] In CO2-rich stream S2, the CO2 content is 99% by mass.

[0108] Example 3

[0109] The system of Example 1 is used.

[0110] Using the method of Example 1, except that the volume flow ratio of the primary gas passage and the secondary gas passage is replaced with 20:80, while the other conditions are the same, high-temperature flue gas P3 and CO2-rich stream S3 are obtained.

[0111] The temperature of the high-temperature flue gas P3 is 118°C, and the CO2 content in the high-temperature flue gas P3 is 25% by mass.

[0112] In CO2-rich stream S3, the CO2 content is 94% by mass.

[0113] Comparative Example 1

[0114] The system of Example 1 is used.

[0115] The method of Example 1 was used, except that the oxygen-enriched gas (oxygen content of 95% by mass and oxygen excess coefficient of 1.1) was replaced with air, while the other conditions were the same, to obtain high-temperature flue gas DP1 and CO2-enriched stream DS1.

[0116] The temperature of the high-temperature flue gas DP1 is 115°C, and the CO2 content in the high-temperature flue gas DP1 is 15% by mass.

[0117] In CO2-rich stream DS1, the CO2 content is 80% by mass.

[0118] Comparative Example 2

[0119] The system of Embodiment 1 is adopted, except that the bottom burner 3 and the side wall burner 4 are each independently provided with an oxygen-enriched gas nozzle 15 and a gas passage 16;

[0120] Using the method of Example 1, high-temperature flue gas DP2 and CO2-rich stream DS2 were obtained;

[0121] The temperature of the high-temperature flue gas DP2 is 110°C, and the CO2 content in the high-temperature flue gas DP1 is 10% by mass.

[0122] In CO2-rich stream DS2, the CO2 content is 85% by mass.

[0123] Compared to Comparative Examples 1-2, the system provided by this invention, by limiting the structure of the burner in the ethylene cracking furnace, allows for the full staged combustion of oxygen-rich gas and natural gas, avoiding the occurrence of local high-temperature areas in the furnace. In particular, by limiting the volume flow ratio of the primary gas passage and the secondary gas passage within the preferred protection range, it is more conducive to increasing the CO2 concentration in the high-temperature flue gas and the CO2 concentration in the CO2-rich stream.

[0124] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An ethylene cracking furnace system, characterized in that, The system includes: an ethylene cracking furnace and a CO2 recovery unit connected in sequence; the ethylene cracking furnace includes: a convection section with a lower opening and a radiation section with an upper opening, and the convection section and the radiation section are connected through the lower opening and the upper opening; the radiation section includes: a cracking furnace tube, a cracking furnace chamber, and at least one burner; each burner is independently equipped with an oxygen-enriched gas nozzle, a primary natural gas channel, and at least one secondary natural gas channel; wherein, the oxygen content in the oxygen-enriched gas is 70-100% by volume; based on the total volumetric flow rate of the natural gas, the volumetric flow rate ratio of the primary natural gas channel to the secondary natural gas channel is 25-45:55-75; The pyrolysis furnace is used to stage the combustion of oxygen-enriched gas and natural gas. The staged combustion products transfer heat to the pyrolysis furnace tubes, and the heat-exchanged products enter the convection section. The convection section is used to exchange heat between the heat-exchanged product and the pyrolysis feedstock to obtain high-temperature flue gas converted from the heat-exchanged product and heated pyrolysis feedstock converted from the pyrolysis feedstock. The CO2 recovery device is used to cool and recover CO2 from the high-temperature flue gas to obtain a CO2-rich stream; the CO2 recovery device includes: a first heat exchanger and a second heat exchanger connected in sequence. The first heat exchanger is used to perform a first heat exchange between the high-temperature flue gas and the first cooling medium to obtain low-temperature flue gas and cooling water; The second heat exchanger is used to perform a second heat exchange on the low-temperature flue gas and the second cooling medium to obtain a CO2-rich stream and exhaust gas; The first cooling medium and the second cooling medium are each independently selected from ethylene and / or propylene.

2. The system according to claim 1, characterized in that, The pyrolysis furnace tube is installed inside the pyrolysis furnace chamber and is used to carry out the pyrolysis reaction of the heated pyrolysis raw material; And / or, the pyrolysis feedstock is selected from at least one of ethane, naphtha, hydrotreated tail oil and diesel.

3. The system according to claim 1, characterized in that, The convection section is equipped with a pyrolysis feedstock inlet and a high-temperature flue gas outlet; And / or, the burner includes a bottom burner and a sidewall burner, respectively disposed at the bottom and sidewall of the radiant section, for introducing the oxygen-enriched gas and natural gas into the pyrolysis furnace; And / or, the ratio of the number of bottom burners to sidewall burners is 1:1.5-3; And / or, the number of the bottom burners is ≥2.

4. The system according to claim 3, characterized in that, The ratio of the number of bottom burners to the number of sidewall burners is 1:2-2.5; And / or, the number of the bottom burners is 2-8.

5. The system according to claim 1, characterized in that, The oxygen-enriched gas nozzle is a cylindrical nozzle and is located on the central axis of the burner; And / or, the upper part of the oxygen-enriched gas nozzle is provided with at least one spray hole; And / or, the number of nozzles is ≥2.

6. The system according to claim 5, characterized in that, The number of nozzles is 3-4.

7. The system according to claim 1, characterized in that, Based on the total volumetric flow rate of the natural gas, the volumetric flow rate ratio of the primary natural gas channel and the secondary natural gas channel is 30-40:60-70; And / or, the cross-sections of the primary natural gas passage and the secondary natural gas passage are each independently selected from circular or rectangular; And / or, the number of the secondary natural gas channels is ≥2.

8. The system according to claim 7, characterized in that, The number of secondary natural gas channels is 4-10.

9. The system according to claim 1, characterized in that, The CO2 recovery device also includes a compressor; And / or, the compressor is disposed between the first heat exchanger and the second heat exchanger for compressing the low-temperature flue gas.

10. The system according to claim 1, characterized in that, The radiation section also includes a quench boiler connected to the pyrolysis furnace tube; And / or, the quench boiler is connected to the top of the pyrolysis furnace tube; And / or, the system further includes: an oxygen supply device connected to the oxygen-enriched gas nozzle; And / or, the oxygen supply device is selected from the air separation unit, water electrolysis unit, and liquid oxygen storage tank in the oil refining unit.

11. A pyrolysis method, characterized in that, The method is performed in the system described in any one of claims 1-10.

12. The method according to claim 11, characterized in that, The method includes the following steps: (1) The oxygen-enriched gas and natural gas are staged combustion in the pyrolysis furnace, and the staged combustion products are transferred to the pyrolysis furnace tubes to obtain the heat exchanged products. (2) The heat exchanged product is introduced into the convection section and the pyrolysis feedstock for heat exchange to obtain high-temperature flue gas transformed from the heat exchanged product and heated pyrolysis feedstock transformed from the pyrolysis feedstock. (3) The high-temperature flue gas is cooled and recovered in the CO2 recovery device of the system to obtain a CO2-rich stream; The heated pyrolysis feedstock is introduced into the pyrolysis furnace tube for pyrolysis reaction; The cooling and recovery process includes: subjecting the high-temperature flue gas to a first heat exchange, and subjecting the resulting low-temperature flue gas to a second heat exchange to obtain the CO2-rich stream; Before the second heat exchange, the low-temperature flue gas is compressed.

13. The method according to claim 12, characterized in that, The CO2-rich logistics contains ≥90% CO2 by mass.

14. The method according to claim 12, characterized in that, In step (2), the temperature of the high-temperature flue gas is 120-130℃; the CO2 concentration in the high-temperature flue gas is 15-40% by mass.

15. The method according to claim 13, characterized in that, The CO2 content in the CO2-rich stream is 96-99% by mass.

16. The method according to claim 14, characterized in that, In step (2), the temperature of the high-temperature flue gas is 125-128℃; the CO2 concentration in the high-temperature flue gas is 20-30% by mass.

17. The method according to claim 12, characterized in that, The mass flow ratio of the oxygen-enriched gas to the natural gas is 0.1-0.5:

1.

18. The method according to claim 17, characterized in that, The mass flow ratio of the oxygen-enriched gas to the natural gas is 0.3-0.4:

1.

19. The method according to claim 12, characterized in that, The oxygen-enriched gas contains 90-100% oxygen by volume; the oxygen excess coefficient is 1-1.

5.

20. The method according to claim 19, characterized in that, The oxygen excess coefficient is 1.1-1.2.

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