Very large cracking furnace

Abstract

This invention relates to the field of pyrolysis furnace technology, specifically to an ultra-large pyrolysis furnace. The pyrolysis furnace includes: N radiant sections, where N is a positive integer and N≥3; a shared convection section is disposed above the N radiant sections in the middle; a transition flue zone is disposed between the N radiant sections and the convection section; wherein the convection section has a hollow annular structure and internally contains heat exchange coils with interconnected structures; wherein the high-temperature flue gas generated by the N radiant sections enters the convection section after passing through the transition flue zone, and exchanges heat with the heat exchange coils to obtain flue gas products converted from the high-temperature flue gas. The pyrolysis furnace provided by this invention avoids the problem of excessively large radiant section spans by rationally arranging the positional relationship between multiple radiant sections and the convection section, and the production capacity of the pyrolysis furnace can be controlled by changing the number of radiant sections and the number of pyrolysis furnace tubes.

Description

Technical Field

[0001] This invention relates to the field of pyrolysis furnace technology, and more specifically, to an ultra-large pyrolysis furnace. Background Technology

[0002] Cracking furnaces are the most important equipment in the production of essential chemical feedstocks such as ethylene, propylene, and butadiene from various gaseous and liquid petroleum fractions, and are the leading equipment in the entire ethylene process industry. The greening, scaling up, and intelligentization of cracking furnaces have always been research directions in the cracking field. Large and ultra-large cracking furnaces will significantly reduce investment and construction costs and the cost per ton of ethylene, facilitate intelligent control of the furnace, and enable centralized treatment of excessive nitrogen oxides. How to rationally configure the relative positions of the convection and radiation sections has become an important direction in the research and development of ultra-large cracking furnaces.

[0003] With the development of the petrochemical industry, the single-furnace production capacity of cracking furnaces has gradually increased from 100,000 tons to 200,000 tons, 300,000 tons, and even 400,000 tons. The increasing production capacity requires maximizing the arrangement of radiant furnace tubes within a given floor space. Currently, large-scale cracking furnaces in operation are mainly single-radiant and double-radiant section furnaces. The furnace tubes within the radiant section are typically arranged in a single row, thus limiting the production capacity of a single furnace chamber. As production capacity gradually expands, especially to over 300,000 tons, the problems of uneven temperature distribution within the cracking furnace and its construction become more prominent, adversely affecting cracking selectivity, fuel consumption, operating cycle, and the lifespan of the radiant furnace tubes.

[0004] To address the aforementioned issues, KBR and KELLOGG successively applied for dual-furnace pyrolysis furnaces that share a single convection section and employ a combination of bottom-firing or bottom-firing and side-firing heating. The radiant section furnace tubes are arranged in a single row, resulting in more uniform heating. This type of pyrolysis furnace has a significant advantage when the production capacity is ≤300,000 tons. However, as the pyrolysis furnace capacity continues to increase, its structural form will be difficult to meet production requirements.

[0005] To address the aforementioned issues, CN1513950A discloses a novel multi-radiation zone pyrolysis furnace. This furnace divides the radiant section into multiple zones via furnace walls, with these zones sharing a single convection section. Bottom burners are distributed along both sides of the furnace walls, ensuring uniform heating of the furnace tubes in the radiant section. However, this structure fails to resolve the problems of different raw materials having different operating cycles within the same pyrolysis furnace, leading to zoned operation and coking in different furnace chambers—specifically, the issues of uniform flue gas distribution and preventing interference between different zones. This ultimately affects the operational stability of the pyrolysis furnace.

[0006] CN104232146A discloses an ethylene cracking furnace in which the arrangement of furnace tubes in the radiant section is changed from a single row to an X-shaped radiant coil module arranged perpendicular to the bottom surface along the length of the furnace body. This is equivalent to connecting multiple double-furnace cracking furnaces in series. However, this structure is relatively complex, has high construction costs, and does not reduce the floor space.

[0007] Meanwhile, for single-radiation section pyrolysis furnaces, when their production capacity is around 100,000 tons, the temperature distribution inside the furnace is relatively uniform, and the NO0.05 of the pyrolysis furnace is low. X Emissions are relatively low, and the construction of cracking furnaces is relatively simple, making them economical. However, as the production capacity of cracking furnaces increases to 150,000 tons, uneven temperature distribution within the furnace becomes more pronounced, leading to high NO levels. X Emissions are increased, and the difficulty and cost of construction are also significantly higher.

[0008] In summary, although dual-furnace cracking furnaces have been applied in actual production, existing cracking furnace technology still has certain problems if production capacity continues to increase. Therefore, there is an urgent need to develop a new type of ultra-large cracking furnace (ethylene production capacity greater than 300,000 tons) to meet future production needs. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned technical problems and provide a novel ultra-large pyrolysis furnace. By rationally setting the positional relationship between the radiation section and the convection section, as well as the arrangement of the heat exchange coils in the convection section, the pyrolysis furnace can ensure the stable operation of each radiation section under different pyrolysis raw materials and operating conditions for a certain period of time; at the same time, it improves the production capacity of the pyrolysis furnace.

[0010] To achieve the above objectives, the present invention provides an ultra-large pyrolysis furnace, which includes: N radiation sections, wherein N is a positive integer and N≥3; a common convection section is arranged above the middle of the N radiation sections; and a transition flue zone is arranged between the N radiation sections and the convection section.

[0011] The convection section is a hollow annular structure with a heat exchange coil having a communicating structure inside.

[0012] The high-temperature flue gas generated in the N radiation sections enters the convection section after passing through the transition flue area, where it exchanges heat with the heat exchange coil to obtain flue gas products transformed from the high-temperature flue gas.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] (1) The cracking furnace provided by the present invention avoids the problem of excessively large span of the radiation section by reasonably arranging the positional relationship between multiple radiation sections and convection sections. The production capacity of the cracking furnace can be controlled by changing the number of radiation sections and the number of cracking furnace tubes. For example, if the cracking furnace is used for ethylene cracking, the production capacity of a single cracking furnace can be significantly increased to more than 400,000 tons of ethylene per year under the premise of low construction cost.

[0015] (2) By limiting the structure of the transition flue and setting the partition plate in the convection section, the present invention ensures that the flue gas entering the convection section from the two adjacent radiation sections has no vortex flow phenomenon, avoids mutual influence of flue gas, and thus the operation of the two adjacent radiation sections will not interfere with each other; at the same time, it significantly improves the operation flexibility and stability of the pyrolysis furnace.

[0016] (3) The pyrolysis furnace provided by the present invention has a wide range of raw material adaptability, and all kinds of raw materials can be pyrolyzed under optimal conditions;

[0017] (4) The pyrolysis furnace provided by this invention has the advantages of uniform heating, high heat transfer rate, stable control system, long operating cycle, and low NO emission. X It features a relatively small production volume; at the same time, the pyrolysis furnace has a compact structure and saves floor space. Attached Figure Description

[0018] Figure 1 This is a cross-sectional schematic diagram of an ultra-large pyrolysis furnace provided by the present invention;

[0019] Figure 2 This is a cross-sectional schematic diagram of an ultra-large pyrolysis furnace provided by the present invention.

[0020] Explanation of reference numerals in the attached figures

[0021] 1. Inner wall of the convection section; 2. Outer wall of the convection section; 3. Radiation section.

[0022] 4. Heat exchanger coil; 5. Convection section; 6. Cracking furnace tube.

[0023] 7. Bottom burner; 8. Quenching boiler; 9. Partition plate.

[0024] 10. Sidewall burner Detailed Implementation

[0025] 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.

[0026] In this invention, unless otherwise specified, the “top” of the container refers to 0-10% of the container from top to bottom; the “upper part” of the container refers to 10-40% of the container from top to bottom; the “middle part” of the container refers to 40-60% of the container from top to bottom; the “lower part” of the container refers to 60-90% of the container from top to bottom; and the “bottom” of the container refers to 90-100% of the container from top to bottom.

[0027] The present invention provides an ultra-large pyrolysis furnace, which includes: N radiation sections, where N is a positive integer and N≥3; a common convection section is arranged above the middle of the N radiation sections; and a transition flue area is arranged between the N radiation sections and the convection section.

[0028] The convection section is a hollow annular structure with a heat exchange coil having a communicating structure inside.

[0029] The high-temperature flue gas generated in the N radiation sections enters the convection section after passing through the transition flue area, where it exchanges heat with the heat exchange coil to obtain flue gas products transformed from the high-temperature flue gas.

[0030] The pyrolysis furnace provided by this invention, through the reasonable configuration of the positional relationship between the radiant section and the convection section, can arrange as many radiant sections as possible within a certain footprint. This not only improves the single-furnace production capacity of the pyrolysis furnace but also solves the problem of excessively large span of the radiant section and facilitates construction. Furthermore, combined with the setting of partition plates and heat exchange coils in the convection section, it can ensure that each radiant section of the pyrolysis furnace can achieve stable operation under different pyrolysis feedstocks and operating conditions (including coking and pyrolysis operations).

[0031] In this invention, unless otherwise specified, the pyrolysis furnace includes N radiant sections and 1 convection section, with the N radiant sections sharing one convection section, and a transition flue zone is provided between the N radiant sections and the convection section.

[0032] According to the present invention, preferably, M partition plates are vertically arranged at the bottom of the convection section, where M is a positive integer and M≥3, for uniformly distributing the high-temperature flue gas generated by the N radiation sections. This arrangement guides the high-temperature flue gas between adjacent radiation sections, ensuring no eddies or flow deviations occur when both adjacent radiation sections are operating normally; and ensures no mixing of the high-temperature flue gas when one radiation section is operating normally while the other is charring, thus improving the overall operational flexibility and stability of the pyrolysis furnace.

[0033] In some embodiments of the present invention, preferably, the number of the partition plates is greater than or equal to the number of the radiation segments.

[0034] In this invention, when the number of partition plates equals the number of radiation sections, the partition plates are vertically disposed at the bottom of the convection section and at the interface between two adjacent radiation sections; when the number of partition plates exceeds the number of radiation sections, the partition plates are disposed not only at the interface between two adjacent radiation sections but also in any region of the convection section corresponding to the radiation section.

[0035] In some embodiments of the present invention, preferably, the ratio of the height of the partition plate to the height of the convection section is 0.01-0.2:1, for example, 0.01:1, 0.05:1, 0.08:1, 0.1:1, 0.12:1, 0.15:1, 0.2:1, and any value within the range of any two values, preferably 0.05-0.15:1. When the height is less than 0.01, the flue gas will mix, resulting in unstable flow of flue gas in the convection section of the pyrolysis furnace. When the height is greater than 0.2, the arrangement of heat exchange tubes in the convection section is reduced, reducing waste heat recovery; or increasing construction difficulty.

[0036] According to the present invention, preferably, the convection section is a hollow cylinder or frustum, more preferably a hollow cylinder.

[0037] According to the present invention, preferably, the convection section includes an inner wall surface and an outer wall surface.

[0038] According to the present invention, preferably, the heat exchange coil is arranged around the central axis of the convection section between the inner wall surface and the outer wall surface of the convection section; more preferably, the arrangement of the heat exchange coil is selected from a circular loop or a rectangular loop.

[0039] According to the present invention, preferably, the temperature of the heat exchange medium inlet is 0-100℃, more preferably 10-70℃; and the temperature of the heat exchange medium outlet is 500-650℃, more preferably 550-630℃. Wherein, the heat exchange medium outlet temperature refers to the inlet temperature of the radiation section.

[0040] According to the present invention, preferably, each of the radiant sections includes at least one pyrolysis furnace tube, at least one burner, and a pyrolysis furnace chamber; more preferably, the pyrolysis furnace tube is vertically arranged inside the pyrolysis furnace chamber.

[0041] According to the present invention, preferably, the radiant section further includes a quench boiler connected to the pyrolysis furnace tube.

[0042] In this invention, the pyrolysis furnace tubes are all conventional pyrolysis furnace tubes in the art.

[0043] In some embodiments of the present invention, preferably, the pyrolysis furnace tubes are arranged in a single row and / or double row; more preferably, the configuration of the pyrolysis furnace tubes is selected from at least one of 2-1, 1-1, 8-4-2-1, 4-2-1-1 and single-pass furnace tubes; wherein, the single-pass furnace tubes are selected from equal-diameter furnace tubes and variable-diameter furnace tubes.

[0044] 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, 1:2.5, 1:3, and any value in any range of any two values, preferably 1:2-2.5.

[0045] In some embodiments of the present invention, preferably, the number of bottom burners is ≥2, and more preferably 2-8.

[0046] According to the present invention, preferably, in each radiation section, the high-temperature flue gas generated by the radiation section transfers heat to the pyrolysis furnace, and the high-temperature flue gas after heat exchange, which is transformed from the high-temperature flue gas, then enters the convection section.

[0047] According to the present invention, preferably, the transition flue region has an inclined structure, the bottom of the transition flue region is connected to the top of N radiation sections, and the top of the transition flue region is connected to the bottom of the convection section; more preferably, the angle α between the central axis of the transition flue region and the horizontal plane is 30-80°, preferably 45-65°.

[0048] According to the present invention, preferably, each of the N radiation segments undergoes a pyrolysis reaction independently; more preferably, at least one of the radiation segments undergoes a charring reaction independently, while the remaining radiation segments undergo a pyrolysis reaction.

[0049] A schematic diagram of the structure of an ultra-large pyrolysis furnace provided by this invention is shown below. Figure 1-2 As stated, by Figure 1-2 It is known that the pyrolysis furnace includes four radiation sections 3, and a common convection section 5 is arranged above the four radiation sections 3. The convection section 5 includes: an inner wall surface 1, an outer wall surface 2, and a heat exchange coil 4. The heat exchange coil 4 is arranged around the central axis of the convection section 5 between the inner wall surface 1 and the outer wall surface 2.

[0050] Among them, a transition flue area is set between the four radiation sections 3 and the convection section 5, and the convection section 5 is a hollow annular structure; four partition plates 9 are vertically set at the bottom of the convection section 5.

[0051] The radiant section 3 includes at least one pyrolysis furnace tube 6, a bottom burner 7, a side wall burner 10, a pyrolysis furnace chamber, and a quench boiler 8 at the top of the pyrolysis furnace tube 6. The pyrolysis furnace tube 6 is vertically arranged inside the pyrolysis furnace chamber. A transition flue zone is provided between the radiant section 3 and the convection section 5.

[0052] The transition flue has an inclined structure, with the bottom of the transition flue connected to the top of N radiation sections 3, and the top of the transition flue connected to the bottom of the convection section 5.

[0053] According to a particularly preferred embodiment of the present invention, the pyrolysis furnace includes: N radiant sections, wherein N is a positive integer and N≥3; a common convection section is disposed above the middle of the N radiant sections; and a transition flue zone is disposed between the N radiant sections and the convection section.

[0054] The convection section is a hollow annular structure with a heat exchange coil having a communicating structure inside.

[0055] Among them, the high-temperature flue gas generated by the N radiation sections enters the convection section after passing through the transition flue area, and exchanges heat with the heat exchange coil to obtain the flue gas products transformed from the high-temperature flue gas;

[0056] The convection section has M partition plates vertically arranged at its bottom, where M is a positive integer and N≥3, used to uniformly distribute the high-temperature flue gas generated by the N radiation sections; the height ratio of the partition plates to the height of the convection section is 0.05-0.15:1.

[0057] The transition flue area has an inclined structure, and the angle α between the central axis of the transition flue area and the horizontal plane is 30-80°.

[0058] The present invention will be described in detail below through embodiments.

[0059] Comparative Example 1

[0060] For example, an ethylene plant with an annual production capacity of 300,000 tons requires two 150,000-ton-per-year cracking furnaces. Each 150,000-ton-per-year cracking furnace consists of two radiant sections. One radiant section has a furnace height of approximately 15 meters and a length of approximately 20 meters. Within the radiant zone, 96 sets of type 1-1 furnace tubes are arranged, with 36 bottom burners symmetrically arranged around the furnace tubes. Naphtha and hydrotreated tail oil can be cracked separately in the two radiant zones. The optimized operating conditions for each feedstock are: naphtha 593℃, outlet temperature 838℃, and radiant zone heat load 96.55 GJ / h; hydrotreated tail oil cross temperature 561℃, outlet temperature 816℃, and radiant zone heat load 100.67 GJ / h. Furthermore, by adjusting the heat supply of each burner, the heat load of different radiant zones can be met. The furnace tubes in both radiant zones are heated uniformly, and the flue gas temperature in the convection zone is uniform, achieving optimal operation for various feedstocks.

[0061] Example 1

[0062] Cracking furnace, such as Figure 1-2 As shown, the ratio of the height of the partition plate to the height of the convection section is 0.1:1; the angle α between the central axis of the transition flue zone and the horizontal plane is 60°.

[0063] A 300,000-ton-per-year cracking furnace comprises four radiant sections, each with a furnace capacity of 75,000 tons. Each section contains 96 sets of type 1-1 furnace tubes, and 36 bottom burners are arranged symmetrically around the furnace tubes, sharing a common convection section. Vertical flue gas distribution plates are located within the convection section. The four radiant sections can crack four feedstocks: ethane, naphtha, diesel, and hydrotreated tail oil. Optimized operating conditions for each feedstock are as follows: ethane furnace: inlet temperature 610℃, outlet temperature 850℃; naphtha furnace: inlet temperature 593℃, outlet temperature 838℃, radiant section heat load 96.55 GJ / h; hydrotreated tail oil furnace: inlet temperature 561℃, outlet temperature 816℃, radiant section heat load 100.67 GJ / h; diesel furnace: inlet temperature 570℃, outlet temperature 825℃.

[0064] Although the process conditions of each radiant section differ significantly, the heat load of different radiant zones can be met by adjusting the heat supply of the bottom burners. The furnace tubes in each zone are heated evenly, and due to the presence of the flue gas distribution plate, separate coking chambers can be used in the pyrolysis furnace, ensuring stable operation. At the same time, because they share a single convection section, a significant amount of investment is saved, which is superior to Comparative Example 1.

[0065] 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 ultra large cracking furnace characterized by, The pyrolysis furnace includes: N radiation sections, where N is a positive integer and N≥3; a shared convection section is provided above the middle of the N radiation sections; and a transition flue area is provided between the N radiation sections and the convection section. The convection section is a hollow cylinder or frustum, and has a heat exchange coil with a communicating structure inside. The high-temperature flue gas generated by the N radiant sections enters the convection section after passing through the transition flue zone, where it exchanges heat with the heat exchange coil to obtain flue gas products transformed from the high-temperature flue gas. The transition flue zone has an inclined structure, with the bottom of the transition flue zone connected to the top of the N radiant sections and the top of the transition flue zone connected to the bottom of the convection section. The bottom of the convection section is vertically equipped with M partition plates, where M is a positive integer and M≥3, which are used to uniformly distribute the high-temperature flue gas generated by the N radiation sections. The number of partition plates is greater than or equal to the number of radiation segments; The ratio of the height of the partition plate to the height of the convection section is 0.01-0.2:1; The convection section includes an inner wall surface and an outer wall surface. The heat exchange coil is arranged around the central axis of the convection section between the inner wall and the outer wall of the convection section.

2. Cracking furnace according to claim 1, characterized in that The ratio of the height of the partition plate to the height of the convection section is 0.05-0.15:

1.

3. The cracker furnace of claim 1, wherein, The convection section is a hollow cylinder.

4. The cracker furnace of claim 1, wherein, The arrangement of the heat exchange coils is selected from circular loops and rectangular loops.

5. Cracking furnace according to any of claims 1-4, characterized in that The heat exchange coil is provided with a heat exchange medium inlet and a heat exchange medium outlet.

6. Cracking furnace according to claim 5, characterized in that The temperature at the inlet of the heat exchange medium is 0-100℃; the temperature at the outlet of the heat exchange medium is 500-650℃.

7. Cracking furnace according to claim 6, characterized in that The temperature at the inlet of the heat exchange medium is 10-70℃; the temperature at the outlet of the heat exchange medium is 550-630℃.

8. Cracking furnace according to any of claims 1-4, characterized in that Each of the radiant sections includes at least one pyrolysis furnace tube, at least one burner, and a pyrolysis furnace chamber.

9. The pyrolysis furnace according to claim 8, characterized in that, The pyrolysis furnace tube is vertically arranged inside the pyrolysis furnace chamber.

10. The cracker furnace of claim 8, wherein, The radiant section also includes a quench boiler connected to the top of the pyrolysis furnace tube.

11. The cracker furnace of claim 8, wherein, The pyrolysis furnace tubes are arranged in a single row and / or double row.

12. The cracker furnace of claim 8, wherein, The burner includes a bottom burner and a sidewall burner, which are respectively disposed at the bottom and sidewall of the radiant section.

13. Cracking furnace according to claim 12, characterized in that The ratio of the number of bottom burners to sidewall burners is 1:1.5-3.

14. Cracking furnace according to claim 13, characterized in that The ratio of the number of bottom burners to sidewall burners is 1:2-2.

5.

15. The cracker furnace of claim 12, wherein, The number of bottom burners is ≥2.

16. The cracker furnace of claim 15, wherein, The number of bottom burners is 2-8.

17. The cracker furnace of claim 8, wherein, In each radiant section, the high-temperature flue gas generated in the radiant section transfers heat to the pyrolysis furnace tube, and the heat-exchanged flue gas then enters the convection section.

18. The pyrolysis furnace according to claim 1, characterized in that, The angle α between the central axis of the transition flue zone and the horizontal plane is 30-80°.

19. The cracker furnace of claim 18, wherein, The angle α between the central axis of the transition flue zone and the horizontal plane is 45-65°.

20. The pyrolysis furnace according to claim 1, characterized in that, Each of the N radiation segments undergoes a fragmentation reaction independently.

21. The cracker furnace of claim 1, wherein, At least one of the radiation sections undergoes a charring reaction independently, while the remaining radiation sections undergo a pyrolysis reaction.

Images