System and method for cascade utilization of waste heat from cracked gas

Abstract

The present invention relates to the technical field of petrochemical cracking furnaces, and discloses a system and method for the cascade utilization of waste heat from cracked gas. The method comprises: feeding a raw material stream and a dilution steam stream into a convection section of a cracking furnace, heating and mixing same, and then feeding same into a radiant section of the cracking furnace for a cracking reaction so as to obtain a cracked gas, wherein the cracked gas is quenched multiple times by using the dilution steam stream and / or combustion materials in the radiant section, thereby achieving the cascade recovery of the heat from the cracked gas. The cracking method and device reduce the consumption of fuel gas and improve the thermal efficiency of cracking furnaces.

Description

A system and method for cascade utilization of waste heat from pyrolysis gas

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Chinese Patent Application No. 202411972232.3, filed on December 30, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of petrochemical cracking furnace technology, specifically to a system and method for the cascade utilization of waste heat from cracked gas. Background Technology

[0004] Ethylene is the most important basic raw material in the petrochemical industry, and its development level is an important indicator of the quality of a country's petrochemical industry development. As a key reaction unit in an ethylene plant, the ethylene cracking furnace accounts for about 70% of the total energy consumption of the entire ethylene plant. Therefore, energy saving and consumption reduction in the cracking furnace directly affect the overall energy consumption level of the ethylene plant.

[0005] Conventional ethylene cracking furnaces produce high-temperature flue gas by mixing combustion gas with air. This flue gas is used to power the cracking reaction, preheat feedstock, and generate ultra-high-pressure steam. The temperature inside the furnace can reach approximately 1200 degrees Celsius, while the air temperature is generally ambient. This significant temperature difference increases energy consumption. To reduce energy consumption, current methods (as shown in Figure 1) primarily involve preheating the air before it enters the burner using quench water, low-pressure steam, or condensate from the ethylene plant, thus saving on fuel gas consumption.

[0006] There is an urgent need for a simplified process for the cascade utilization of waste heat from pyrolysis furnaces. Under the premise of ensuring the stable operation of the pyrolysis furnace, the waste heat from the top flue gas and the waste heat from the pyrolysis gas can be efficiently utilized by optimizing the process flow, thereby reducing fuel gas consumption and improving the thermal efficiency of the pyrolysis furnace. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem that existing technologies cannot maximize the utilization of the waste heat of the pyrolysis furnace itself, and to provide a pyrolysis method and pyrolysis device that utilizes the waste heat of the pyrolysis furnace in stages. This pyrolysis method and device reduce fuel gas consumption and improve the thermal efficiency of the pyrolysis furnace.

[0008] To achieve the above objectives, the present invention provides a pyrolysis method that utilizes the waste heat of a pyrolysis furnace in stages. The raw material stream and the dilution steam stream are fed into the convection section of the pyrolysis furnace for heating and mixing, and then fed into the radiation section of the pyrolysis furnace for pyrolysis reaction to obtain pyrolysis gas. The pyrolysis gas is subjected to multiple rapid coolings using the dilution steam stream and / or the combustion material in the radiation section, thereby recovering the heat of the pyrolysis gas in stages.

[0009] As shown in Figures 2-5, a second aspect of the present invention provides a pyrolysis apparatus, which includes:

[0010] The pyrolysis furnace includes a convection section and a radiation section, wherein the convection section is used to heat and mix the raw material stream 1 and the dilution steam stream 5 and send them into the radiation section for pyrolysis reaction to obtain pyrolysis gas stream 10;

[0011] The quencher includes a first quencher K, a second quencher L and a third quencher O connected in series through a cracked gas pipeline. The quencher is used to quench the cracked gas stream 10 multiple times and recover the heat of the cracked gas stream 10 in stages.

[0012] A preheater, connected to the shell side of the quencher, is used to preheat and dilute the cracked gas dilution steam stream 5 and / or the air stream 22 before it enters the radiation section.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects:

[0014] 1. The waste heat of the pyrolysis furnace itself is used to preheat the feed material of the pyrolysis furnace, which reduces fuel gas consumption and improves the thermal efficiency of the pyrolysis furnace.

[0015] 2. Reducing carbon dioxide emissions aligns with the national guidelines for energy conservation and emission reduction;

[0016] 3. The process flow has been optimized, making it easier to implement. Attached Figure Description

[0017] Figure 1 is a process flow diagram of a traditional steam cracking furnace.

[0018] Figure 2 is a flowchart of a preferred embodiment of the present invention, which describes a pyrolysis method that utilizes waste heat from a pyrolysis furnace in stages.

[0019] Figure 3 is a flowchart of a preferred embodiment of the present invention, which describes a pyrolysis method that utilizes waste heat from a pyrolysis furnace in stages.

[0020] Figure 4 is a flowchart of a preferred embodiment of the present invention, namely, Scheme 3, of a pyrolysis method that utilizes waste heat from a pyrolysis furnace in stages.

[0021] Figure 5 is a flowchart of a preferred embodiment of the present invention, namely, Scheme 4, of a pyrolysis method that utilizes waste heat from a pyrolysis furnace in stages.

[0022] See the embodiments for the explanation of the reference numerals in the attached figures. Detailed Implementation

[0023] 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.

[0024] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "left," and "right" generally refer to the upper, lower, left, and right positions shown in the accompanying drawings; "inner" and "outer" refer to the inner and outer positions relative to the outline of each component itself; and "upper," "lower," "top," and "bottom" are generally descriptive terms describing the relative positions of the components in relation to the directions shown in the accompanying drawings or in relation to the vertical, perpendicular, or gravitational directions.

[0025] In this invention, "device" refers to a unit composed of various components that have the same function and / or perform related functions.

[0026] In the description of this application, it should be understood that, unless otherwise specified, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0027] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0028] In this invention, the raw material stream includes, but is not limited to, hydrotreated tail oil, diesel, naphtha, light hydrocarbons, LPG, propane, ethane, and other raw materials.

[0029] The first aspect of the present invention provides a pyrolysis method for utilizing the waste heat of a pyrolysis furnace in stages. The raw material stream and the dilution steam stream are fed into the convection section of the pyrolysis furnace for heating and mixing, and then fed into the radiation section of the pyrolysis furnace for pyrolysis reaction to obtain pyrolysis gas. The pyrolysis gas is subjected to multiple rapid coolings using the dilution steam stream and / or the combustion material in the radiation section, thereby recovering the heat of the pyrolysis gas in stages.

[0030] In this invention, the pyrolysis gas is subjected to multiple rapid cooling processes, which can fully utilize the residual heat of the pyrolysis gas and improve the thermal efficiency of the pyrolysis furnace. The feed stream of the pyrolysis furnace includes raw material stream, dilution steam stream, raw material and dilution steam mixture stream, and air stream. In order to reduce viscosity and prevent coking, in some embodiments of this invention, raw material and dilution steam are introduced into the convection section of the pyrolysis furnace, and the flow rate of the dilution steam stream can be 1 to 80 wt% of the raw material stream flow rate.

[0031] As is known to those skilled in the art, the flue gas temperature varies at different locations in the convection section of the pyrolysis furnace. Changes in the process flow will alter the heat distribution of the flue gas. This invention selects the flue gas at the furnace top for heat exchange and recovery, but this does not limit the scope of the invention. When changing the heat exchange location, temperature-level matching is required, and coupled calculations must be performed between the convection section and the radiation section to ensure stable operation of the device during heat extraction and to achieve the optimal product yield. According to one embodiment of the invention, the combustion materials in the radiation section include fuel gas and air. In the presence of air, the fuel gas is burned in the radiation section to obtain flue gas. The flue gas rises along the convection section to the furnace top, where it exchanges heat with the air before entering the radiation section and the flue gas at the furnace top. Using preheated air and fuel gas to burn in the radiation section provides the heat required by the pyrolysis furnace, which can improve the combustion efficiency of the combustion gas.

[0032] According to one embodiment of the present invention, heat exchange is performed using a heat exchange medium during multiple rapid cooling processes.

[0033] According to one embodiment of the present invention, the heat exchange medium is selected from molten salt and / or heat transfer oil.

[0034] According to one embodiment of the present invention, heat transfer oil is used as the heat exchange medium to exchange heat with the flue gas at 100-340°C at the top of the furnace, and then to exchange heat with the air before entering the radiation section.

[0035] According to one embodiment of the present invention, the heat transfer oil exchanges heat with the pyrolysis gas at a temperature below 340°C during multiple rapid cooling processes.

[0036] According to one embodiment of the present invention, molten salt exchanges heat with pyrolysis gas at 300-1200°C during multiple rapid cooling processes.

[0037] According to one embodiment of the present invention, the molten salt is selected from one or more of chloride salts, nitrate salts, fluoride salts and carbonate salts.

[0038] According to one embodiment of the present invention, the heat transfer oil is selected from at least one of alkylnaphthalene type, biphenyl and diphenyl ether low-melting-point mixture type, alkyl diphenyl ether type heat transfer oil or mineral type heat transfer oil.

[0039] According to one embodiment of the present invention, the chloride salt includes lithium chloride and / or potassium chloride.

[0040] According to one embodiment of the present invention, the nitrate is selected from at least one of sodium nitrate, sodium nitrite, or potassium nitrate.

[0041] According to one embodiment of the present invention, the fluoride salt is selected from at least one of lithium fluoride, beryllium fluoride, or thorium fluoride.

[0042] According to one embodiment of the present invention, the carbonate is selected from sodium carbonate and / or potassium carbonate.

[0043] According to one embodiment of the present invention, in the pyrolysis method, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling in sequence, wherein...

[0044] A rapid cooling process allows the pyrolysis gas to exchange heat with the steam drum stream;

[0045] The secondary quenching allows the cracked gas after the first quenching to exchange heat with the dilution steam stream;

[0046] The three rapid cooling processes allow the cracked gas after the second rapid cooling to exchange heat with the air before entering the radiation section.

[0047] According to one embodiment of the present invention, in the pyrolysis method, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling in sequence, wherein...

[0048] A rapid cooling process allows the pyrolysis gas to exchange heat with the air before entering the radiation section.

[0049] Secondary quenching allows the cracked gas from the first quenching to exchange heat with the steam drum stream;

[0050] The three rapid cooling processes allow the pyrolysis gas after the second rapid cooling to exchange heat with the boiler feedwater stream.

[0051] In one embodiment of the present invention, during the initial quenching of the pyrolysis gas, the heat exchange for the initial quenching employs a heat exchange medium. The heat exchange medium first exchanges heat with the pyrolysis gas, and then exchanges heat with the air before it enters the radiation section. Preferably, the heat exchange medium exchanges heat with the mixture of raw material and dilution steam before exchanging heat with the air before entering the radiation section. Using the above embodiment can effectively improve the thermal efficiency of the pyrolysis furnace.

[0052] According to one embodiment of the present invention, the boiler feedwater first exchanges heat with the economizer and then exchanges heat with the pyrolysis gas after secondary rapid cooling.

[0053] According to one embodiment of the present invention, in the pyrolysis method, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling in sequence, wherein...

[0054] A rapid cooling process allows the pyrolysis gas to exchange heat with the air before entering the radiation section.

[0055] Secondary quenching allows the cracked gas from the first quenching to exchange heat with the steam drum stream;

[0056] The three rapid cooling processes allow the cracked gas after the second rapid cooling to exchange heat with the air before entering the radiation section.

[0057] In this invention, during the first quenching of the cracked gas, a heat exchange medium is used for the heat exchange. The heat exchange medium first exchanges heat with the cracked gas, and then with the air before it enters the radiation section. Preferably, the heat exchange medium exchanges heat with the mixture of raw material and dilution steam before exchanging heat with the air before entering the radiation section. Using the above embodiment, the heat recovered from the first quenching heat exchange is sufficient. After being used to preheat the mixture of raw material and dilution steam, a portion of the heat is absorbed by the waste heat absorption medium before being used to preheat the air, achieving full utilization of the recovered heat. Furthermore, the heat recovered from the third quenching heat exchange is also fully utilized by absorbing a portion of the heat with the waste heat absorption medium before being used to preheat the air. Preferably, the preheating absorption medium is heat transfer oil and / or molten salt.

[0058] According to one embodiment of the present invention, the high-pressure steam stream generated by the steam drum is fed into the convection section of the pyrolysis furnace for superheating and then exchanges heat with the high-pressure boiler feedwater stream generated by the steam drum; then the high-pressure steam stream is fed back into the convection section of the pyrolysis furnace for superheating.

[0059] According to one embodiment of the present invention, in the pyrolysis method, when the amount of flue gas produced by the pyrolysis reaction is less than 500 Am. 3 At a rate of / h, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling sequentially, wherein...

[0060] A rapid cooling process allows the pyrolysis gas to exchange heat with the air before entering the radiation section.

[0061] Secondary quenching involves cooling and regulating the temperature of the pyrolysis gas after the first quenching.

[0062] The three rapid cooling processes allow the cracked gas after the second rapid cooling to exchange heat with the air before entering the radiation section.

[0063] According to one embodiment of the present invention, the heat exchange in the primary quenching process uses a heat exchange medium. The heat exchange medium first exchanges heat with the cracked gas, and then exchanges heat with the air before entering the radiation section. Preferably, the heat exchange medium exchanges heat with the mixture of raw material and dilution steam before exchanging heat with the air before entering the radiation section.

[0064] According to one embodiment of the present invention, heat exchange is first performed with a residual heat absorption medium before heat exchange with the air entering the radiation section.

[0065] According to one embodiment of the present invention, the temperature control is to reduce the temperature of the pyrolysis gas after secondary quenching to below 300°C.

[0066] Referring to Figures 2-5 as examples, but not limited to Figures 2-5, a second aspect of the present invention provides a pyrolysis apparatus, the pyrolysis apparatus comprising:

[0067] The pyrolysis furnace includes a convection section and a radiation section. The convection section is used to heat and mix the raw material stream 1 and the dilution steam stream 5 and send them into the radiation section for pyrolysis reaction to obtain pyrolysis gas stream 10. The quench cooler includes a first quench cooler K, a second quench cooler L, and a third quench cooler O connected in series through a pyrolysis gas pipeline. The quench cooler is used to quench the pyrolysis gas stream 10 multiple times and recover the heat of the pyrolysis gas stream 10 in stages. The preheater is connected to the shell side of the quench cooler and is used to preheat the dilution steam stream 5 and / or the air stream 22 before entering the radiation section.

[0068] According to one embodiment of the present invention, as shown in Figures 2 and 4, the preheater includes a raw material and / or dilution steam preheater T and an air preheater S; a flue gas heat exchange section P is provided on the top of the pyrolysis furnace and connected to the air preheater S; the outlet of the air preheater S is connected to the inlet of the radiation section, preferably through a heat exchange medium pipeline.

[0069] According to one embodiment of the present invention, as shown in FIG2, the steam drum N and the shell side of the first quencher K form a circulation loop;

[0070] The shell side of the second quench cooler L is connected in series with the dilution steam preheating section F on the dilution steam feed line;

[0071] The third quencher O is connected to the air preheater S via a heat exchange medium pipeline.

[0072] According to one embodiment of the present invention, as shown in FIG3, the first quench cooler K is connected to the air preheater S through a heat exchange medium pipeline.

[0073] The steam drum N and the shell side of the second quencher L form a circulation loop;

[0074] The third quencher O is connected to the steam drum N via a boiler feedwater pipeline.

[0075] According to one embodiment of the present invention, as shown in FIG3, a raw material and / or dilution steam preheater T is provided on the heat exchange medium pipeline between the first quencher K and the air preheater S.

[0076] According to one embodiment of the present invention, as shown in FIG3, the boiler feedwater flow pipeline passes through economizer section C.

[0077] According to one embodiment of the present invention, as shown in FIG4, the first quench cooler K is connected to the air preheater S through a heat exchange medium pipeline.

[0078] The steam drum N and the shell side of the second quencher L form a circulation loop;

[0079] The third quencher O is connected to the air preheater S via a heat exchange medium pipeline.

[0080] According to one embodiment of the present invention, as shown in FIG4, a raw material and / or dilution steam preheater T is provided on the heat exchange medium pipeline between the first quencher K and the air preheater S.

[0081] According to one embodiment of the present invention, as shown in FIG4, a waste heat recovery heat exchanger U is provided on the heat exchange medium pipeline between the raw material and / or dilution steam preheater T and the air preheater S.

[0082] According to one embodiment of the present invention, as shown in FIG4, a waste heat recovery heat exchanger U is provided on the heat exchange medium pipeline between the air preheater S and the third quencher O.

[0083] According to one embodiment of the present invention, as shown in Figures 2-4, the discharge end of the steam drum N is connected to the feed end of the high-pressure steam superheating section i G, the discharge end of the high-pressure steam superheating section i G is connected to the feed end of the high-pressure steam superheating section ii H through a pipeline equipped with a desuperheater J, the feed end of the desuperheater J is connected to the high-pressure boiler feedwater pipe, and the discharge end of the high-pressure steam superheating section ii H is provided with a high-pressure steam discharge pipe.

[0084] According to one embodiment of the present invention, as shown in FIG5, the first quench cooler K is connected to the air preheater S through a heat exchange medium pipeline.

[0085] The third quencher O is connected to the air preheater S via a heat exchange medium pipeline.

[0086] According to one embodiment of the present invention, as shown in FIG5, a raw material and / or dilution steam preheater T is provided on the heat exchange medium pipeline between the first quencher K and the air preheater S.

[0087] According to one embodiment of the present invention, as shown in FIG5, a waste heat recovery heat exchanger U is provided on the heat exchange medium pipeline between the raw material and / or dilution steam preheater T and the air preheater S.

[0088] According to one embodiment of the present invention, as shown in FIG5, a waste heat recovery heat exchanger U is provided on the heat exchange medium pipeline between the air preheater S and the third quencher O.

[0089] The convection section is provided from top to bottom as follows: flue gas heat exchange section P, raw material preheating section i B, economizer section C including economizer, raw material preheating section ii D, raw material and dilution steam mixing section i E, dilution steam preheating section F, high-pressure steam superheating section i G, high-pressure steam superheating section ii H, and raw material and dilution steam mixing section ii I.

[0090] In an embodiment of the present invention:

[0091] The flue gas heat exchange section P is used to recover heat from the flue gas to heat the heat transfer oil.

[0092] The raw material preheating section B is used to preheat the raw material flow.

[0093] Economizer section C is used to preheat boiler feedwater;

[0094] The raw material preheating stage D is used to preheat the raw material flow.

[0095] The raw material and dilution steam mixing section E is used to heat the raw material and dilution steam streams.

[0096] The dilution steam preheating section F is used to superheat and dilute the steam stream.

[0097] The high-pressure steam superheating section G is used to heat the high-pressure steam stream.

[0098] The high-pressure steam superheating stage II (H) is used to heat the high-pressure steam stream.

[0099] Section I, which mixes raw materials with dilution steam, is used to heat the raw material and dilution steam streams.

[0100] This invention integrates the traditional steam cracking process while also taking into account the energy-saving and consumption-reducing requirements of the cracking furnace. It is suitable for both new and renovation projects, improves design quality, and saves on project investment.

[0101] The advantages of the present invention will be illustrated below through examples of ethylene cracking, but the present invention is not limited thereto.

[0102] Comparative Example

[0103] Figure 1. Labeling: A. Radiant section of pyrolysis furnace; B. Raw material preheating section i; C. Economizer section; D. Raw material preheating section II; E. Raw material and dilution steam mixing section i; F. Dilution steam preheating section; G. High-pressure steam superheating section i; H. High-pressure steam superheating section ii; I. Raw material and dilution steam mixing section ii; J. Desuperheater; K. First quench cooler; L. Second quench cooler; M. Raw material / dilution steam mixer; N. Steam drum; R. Air preheater. 1. Raw material flow; 2. Raw material flow after preheating stage I; 3. Raw material flow after preheating stage II; 4. Raw material / dilution mixture flow; 5. Raw material and dilution steam mixing stage I flow; 6. Total dilution steam flow; 7. Superheated dilution steam flow; 8. Raw material and dilution steam mixing stage II flow; 9. Cracking gas flow; 10. Cracking gas flow after the first quench cooler; 11. Cracking gas flow after the second quench cooler; 13. Boiler feedwater flow; 14. Boiler feedwater flow after the economizer; 15. Boiler feedwater flow after the second quench cooler; 16. High-pressure steam flow; 17. High-pressure boiler feedwater flow; 18. High-pressure steam superheating stage I flow; 19. Desuperheating flow; 20. High-pressure steam superheating stage II flow; 22. Air flow; 23. Preheated air flow; 24. Fuel gas flow; 25. Low-pressure steam or quench water flow; 26. Low-pressure steam or quench water flow after preheating air.

[0104] As can be seen from Figure 1, the radiant section A of the pyrolysis furnace is located below the convection section. A bottom burner is installed in the radiant section A of the pyrolysis furnace, and the high-temperature flue gas generated by fuel combustion flows from bottom to top through the convection section.

[0105] The convection sections, arranged from top to bottom according to their different functions, include: B. Raw material preheating section i; C. Economizer section; D. Raw material preheating section II; E. Raw material and dilution steam mixing section i; F. Dilution steam preheating section; G. High-pressure steam superheating section i; H. High-pressure steam superheating section ii; and I. Raw material and dilution steam mixing section ii.

[0106] The process flow of existing technologies:

[0107] As shown in Figure 1, the raw material stream first enters the raw material preheating section B for preheating, then enters the raw material preheating section D for further preheating, and then enters the mixer M to mix with dilution steam; the dilution steam stream first enters the dilution steam preheating section F, and then enters the mixer M to mix with the raw material.

[0108] The raw material / dilution mixture, after being mixed in mixer M, first enters section E (raw material and dilution steam mixing section i) for heating, and then enters section I (raw material and dilution steam mixing section ii) for superheating. It is then sent to the radiation section for pyrolysis, becoming pyrolyzed gas, which is then discharged. The pyrolyzed gas passes through the first quench cooler K and the second quench cooler L before being sent to subsequent processes.

[0109] Meanwhile, existing technology sets up an economizer section C in the convection section. The boiler feedwater stream sent into the steam drum N is first preheated by the economizer and then enters the shell side of the second quench cooler L. In the second quench cooler L, the boiler feedwater absorbs the heat of the cracked gas and is heated before being sent into the steam drum N.

[0110] Furthermore, because high-quality high-pressure steam is needed to drive the large rotating unit of the steam cracking furnace, high-pressure steam is first produced in the steam drum N. This high-pressure steam then enters the high-pressure steam superheating section i (G), is temperature-controlled by the desuperheater J, and finally enters the high-pressure steam superheating section ii (H) to produce high-quality high-pressure steam. As shown in Figure 1, the high-pressure steam superheating sections i and ii are located in the convection section, which itself consumes a large amount of heat from the convection section.

[0111] In existing technologies, air preheating in cracking furnaces is mainly achieved by drawing quench water, low-pressure steam, or condensate from the external ethylene unit to preheat the air before it enters the burner, thereby saving fuel gas consumption. However, this approach cannot maximize the use of the residual heat of the cracking furnace itself to improve its thermal efficiency.

[0112] In the following embodiments:

[0113] Process flow:

[0114] 1. Raw material stream 1 enters the raw material preheating section B of the cracking furnace and undergoes preliminary preheating to obtain stream 2.

[0115] 2. And further fed into the raw material preheating stage D for preheating;

[0116] 3. The dilution steam stream 5 or 6 is superheated through the dilution steam preheating section F or the second quench cooler L;

[0117] 4. The preheated raw material stream and the dilution steam stream enter the raw material / dilution steam mixer M for thorough mixing to obtain the raw material / dilution mixture stream 4, which is then sent to the raw material and dilution steam mixing section i E, and further superheated in the raw material and dilution steam mixing section ii I before being sent to the pyrolysis furnace radiation section A to undergo a pyrolysis reaction, finally obtaining the pyrolysis gas stream 10.

[0118] 5. The pyrolysis gas stream is further cooled by heat exchange in the first, second, and third quench coolers before being sent to the downstream separation unit.

[0119] Public works side process:

[0120] 1. The boiler feedwater flows through the economizer section (Plan 2 feedwater 13, Plan 13 feedwater 15) or is directly fed into the steam drum N;

[0121] 2. The boiler feedwater in the steam drum N is vaporized by heat exchange in the first quench cooler K and then returned to the steam drum, forming a thermosiphon system;

[0122] 3. The high-pressure steam stream 16 produced from the steam drum is sent to the high-pressure steam superheating stage I and the high-pressure steam superheating stage II for superheating and then sent to the high-pressure steam pipeline network (stream 20);

[0123] Example 1

[0124] This embodiment uses the ethylene cracking furnace system shown in Figure 2, wherein: A, cracking furnace radiant section; B, feedstock preheating section i; C, economizer section; D, feedstock preheating section II; E, feedstock and dilution steam mixing section i; F, dilution steam preheating section; G, high-pressure steam superheating section i; H, high-pressure steam superheating section ii; I, feedstock and dilution steam mixing section ii; J, desuperheater; K, first quench cooler; L, second quench cooler; M, feedstock / dilution steam mixer; N, steam drum; O, third-stage quench heat exchanger; P, flue gas heat exchange section; Q, thermal oil pump; R, thermal oil storage tank; S, air preheater.

[0125] Figure 2 shows the logistics markings: 1. Raw material flow; 2. Raw material flow after the first preheating stage; 3. Raw material flow after the second preheating stage; 4. Raw material / dilution mixture flow; 5. Dilution steam flow; 6. Superheated dilution steam flow after the second quench cooler; 7. Flow after the superheated dilution steam stage; 8. Flow after the first stage of raw material and dilution steam mixing; 9. Flow after the second stage of raw material and dilution steam mixing; 10. Cracking gas flow; 11. Cracking gas flow after the first quench cooler; 12. Cracking gas flow after the second quench cooler; 13. Cracking gas flow after the third quench cooler; 15. Boiler feedwater flow after the economizer. 16. High-pressure steam flow; 17. High-pressure boiler feedwater flow; 18. Flow through high-pressure steam superheating stage I; 19. Flow through desuperheater cooling stage; 20. Flow through high-pressure steam superheating stage II; 22. Air flow; 23. Preheated air flow; 24. Fuel gas flow; 31. Flow into heat transfer oil pump; 32. Heat transfer oil flow after pump; 33. Flow into flue gas heat exchange stage; 34. Heat transfer oil flow after heat exchange with flue gas; 35. Flow to third-stage cold heat exchanger; 36. Flow for heat exchange with third quench cooler; 37. Flow into air preheater; 38. Flow after heat exchange with air.

[0126] Heat transfer oil side process:

[0127] 1. The heat transfer oil medium is stored in the heat transfer oil storage tank R and is transported to the flue gas heat exchange section P and the third quencher O by the heat transfer oil pump Q. After heat exchange, the heated heat transfer oil streams 34 and 36 are obtained respectively.

[0128] 2. Heat transfer oil streams 34 and 36 are combined into stream 37 and sent to air preheater S to heat air stream 22. The heated air 23 is then mixed with fuel gas stream 24 and combusted to release heat, providing the heat required by the pyrolysis furnace.

[0129] In this embodiment, heat from the third quencher is recovered via thermal oil for preheating air. The preheated air is then mixed with fuel gas in the radiant section for combustion, reducing fuel gas consumption by 8%. This embodiment also reduces the demand for high-pressure steam, so the boiler feedwater stream is directly fed into the steam drum. The boiler feedwater stream no longer needs to enter the second quencher to cool the cracked gas. Therefore, the dilution steam stream, which is directly fed into the convection section for heating, is sent to the shell side of the second quencher. Through these settings, without wasting heat or reducing thermal efficiency, the temperature of the boiler feedwater stream is lowered, and the heat sent into the steam drum is reduced. This results in less ultra-high-pressure steam production. Furthermore, preheating the dilution steam stream reduces the demand for high-temperature flue gas in the convection section.

[0130] A flue gas heat exchange section P is set at the top of the convection section, and heat transfer oil is used to recover the heat of the flue gas to preheat the air, which reduces fuel gas consumption by 4% compared with existing technologies.

[0131] In existing technologies, external heat sources preheat fuel gas and / or air, requiring less fuel to achieve the same heating effect in the radiation section, thus saving fuel. However, this also leads to a decrease in the production of high-temperature flue gas and a reduction in the total energy of the convection section. Furthermore, the boiler feedwater stream that was originally introduced to the shell side of the second quencher has been changed to a dilution steam stream, resulting in a decrease in heat exchange capacity. The cooling effect of the pyrolysis gas deteriorates. This invention utilizes a third quencher for further cooling and heat absorption.

[0132] Example 2

[0133] This embodiment uses the ethylene cracking furnace system shown in Figure 3, wherein: A, cracking furnace radiant section; B, feedstock preheating section i; C, economizer section; D, feedstock preheating section II; E, feedstock and dilution steam mixing section i; F, dilution steam preheating section; G, high-pressure steam superheating section i; H, high-pressure steam superheating section ii; I, feedstock and dilution steam mixing section ii; J, desuperheater; K, first quench cooler; L, second quench cooler; M, feedstock / dilution steam mixer; N, steam drum; W, molten salt transfer pump; V, molten salt storage tank; S, air preheater; T, feedstock / dilution steam preheater.

[0134] Figure 3 shows the logistics markings: 1. Raw material flow; 2. Raw material flow after the first stage of raw material preheating; 3. Raw material flow after the second stage of raw material preheating; 4. Raw material / dilution mixture flow; 6. Dilution steam flow; 7. Flow after the dilution steam superheating stage; 8. Flow after the first stage of raw material and dilution steam mixing; 9. Flow after the second stage of raw material and dilution steam mixing; 10. Cracking gas flow; 11. Cracking gas flow after the first quench cooler; 12. Cracking gas flow after the second quench cooler; 13. Boiler feedwater flow; 14. Flow after... 16. Feedwater from the economizer boiler; 17. High-pressure steam; 18. Feedwater from the high-pressure boiler; 19. Flow through the high-pressure steam superheating stage I; 20. Flow through the desuperheater; 21. Flow through the high-pressure steam superheating stage II; 22. Air; 23. Preheated air; 24. Fuel gas; 35. Flow into the molten salt pump; 36. Flow after pump; 37. Flow after heat exchange with cracked gas; 38. Flow after preheating raw materials and dilution steam; 39. Flow out of the air preheater.

[0135] Molten salt side process:

[0136] 1. Molten salt medium is stored in molten salt storage tank V, and the molten salt transfer pump W transports the stream 32 to the first quench cooler K. After heat exchange, heated molten salt stream 33 is obtained.

[0137] 2. The temperature of molten salt stream 33 can reach over 600 degrees Celsius. If the temperature of the preheated air is too high, it is first sent to the raw material / dilution steam preheater T to preheat the mixture of raw material and dilution steam stream 8. After the molten salt stream cools down, it becomes stream 34, which is sent to the air preheater S to heat the air stream 22. The heated air 23 is then mixed with the fuel gas stream 24 and combusted to release heat, providing the heat required by the pyrolysis furnace.

[0138] In this embodiment, the heat of the first quencher is recovered by molten salt, and this heat is used in stages to preheat the raw materials / diluted steam flow and then to preheat the air. The recovered heat is fully utilized, and compared with the prior art, the fuel gas consumption can be reduced by 10%, thus achieving the beneficial effect of reducing the energy consumption of the device.

[0139] Example 3

[0140] This embodiment is a combination of Embodiment 1 and Embodiment 2, as shown in Figure 4. In this embodiment, A is the radiant section of the pyrolysis furnace; B is the raw material preheating section i; C is the economizer section; D is the second raw material preheating section; E is the raw material and dilution steam mixing section i; F is the dilution steam preheating section; G is the high-pressure steam superheating section i; H is the high-pressure steam superheating section ii; I is the raw material and dilution steam mixing section ii; J is the desuperheater; K is the first quench cooler; L is the second quench cooler; M is the raw material / dilution steam mixer; N is the steam drum; P is the flue gas heat exchange section; R is the thermal oil storage tank; S is the air preheater; T is the raw material / dilution steam preheater; U is the molten salt waste heat recovery heat exchanger; V is the molten salt storage tank; and W is the molten salt pump.

[0141] Figure 4 shows the logistics markings: 1. Raw material logistics; 2. Raw material logistics after the first stage of preheating; 3. Raw material logistics after the second stage of preheating; 4. Raw material / dilution mixture flow; 6. Dilution steam flow; 7. Flow after the dilution steam superheating stage; 8. Flow after the first stage of mixing raw material and dilution steam; 9. Flow after the second stage of mixing raw material and dilution steam; 10. Cracked gas flow; 11. Cracked gas flow after the first quench cooler; 12. Cracked gas flow after the second quench cooler; 15. Boiler feedwater flow; 16. High-pressure steam flow; 17. High-pressure boiler feedwater flow; 18. Flow after the first stage of high-pressure steam superheating; 19. Flow after the desuperheater cooling stage; 20. Flow after the high-pressure steam... 21. Steam superheating stage II; 22. Air flow; 23. Preheated air flow; 24. Fuel gas flow; 31. Flow into the heat transfer oil pump; 32. Heat transfer oil flow after pump; 33. Flow into the flue gas heat exchange section; 34. Heat transfer oil flow after heat exchange with flue gas; 35. Flow to the third-stage cold heat exchanger; 36. Flow for heat exchange with the third quench cooler; 37. Flow into the molten salt waste heat recovery heat exchanger; 38. Flow into the air preheater; 39. Flow after heat exchange with air; 42. Flow into the molten salt pump; 43. Flow after pump; 44. Flow after heat exchange with cracked gas; 45. Flow after preheating raw materials and dilution steam; 46. Flow out of the molten salt waste heat recovery heat exchanger.

[0142] Combining heat transfer oil with molten salt process:

[0143] 1. The heat transfer oil medium is stored in the heat transfer oil storage tank R and is transported to the flue gas heat exchange section P and the third quencher O by the heat transfer oil pump Q. After heat exchange, the heated heat transfer oil streams 34 and 36 are obtained respectively.

[0144] 2. Heat transfer oil streams 34 and 36 are combined into stream 37. Stream 37 is sent to the molten salt waste heat recovery heat exchanger U and heated by the molten salt stream 45 to obtain stream 38. Stream 38 is sent to the air preheater S to heat the air stream 22. The heated air 23 is mixed with the fuel gas stream 24 and then combusted to release heat, providing the heat required by the pyrolysis furnace.

[0145] 3. Molten salt medium is stored in molten salt storage tank V, and the molten salt transfer pump W transports the stream 43 to the first quench cooler K. After heat exchange, heated molten salt stream 44 is obtained.

[0146] 4. The temperature of molten salt stream 44 can reach over 600 degrees Celsius. If the preheated air temperature is too high, it is first sent to the raw material / dilution steam preheater T to preheat the mixture of raw material and dilution steam stream 8. After the molten salt stream cools down, the resulting stream 45 is sent to the molten salt waste heat recovery heat exchanger U to heat the heat transfer oil stream 37. Alternatively, air can be directly heated through stream 47.

[0147] In this embodiment:

[0148] 1. Boiler feedwater is directly fed into the steam drum; in this scheme, the economizer is no longer installed in the convection section, and the boiler feedwater is directly fed into the steam drum. Therefore, the heat sent into the steam drum is greatly reduced, which reduces the production of high-pressure steam and the heat exchange of cracked gas. The present invention further cools and absorbs heat through a third quench cooler.

[0149] 2. The air is preheated and then sent into the radiant section for combustion. In this scheme, the economizer is no longer installed in the convection section, and the heat of the high-temperature flue gas is not fully utilized. Therefore, a flue gas heat exchange section P is installed at the top of the convection section, and the heat exchange medium is heat transfer oil. The heat of this part of the flue gas is used to heat the air through the heat transfer oil.

[0150] 3. The raw material and dilution steam mixture is preheated before being sent to the convection section. This scheme recovers the heat of the first quencher through molten salt, and utilizes this heat in stages to preheat the raw material / dilution steam stream and then the air, making full use of the recovered heat.

[0151] Because the feed stream to the pyrolysis furnace is preheated, the following beneficial effects are achieved:

[0152] Preheating the air reduces the amount of fuel needed to achieve the same heating effect in the radiant section of the pyrolysis furnace, thus saving fuel. However, this also results in a decrease in the production of high-temperature flue gas, leading to a reduction in the total energy output of the convection section.

[0153] Therefore, heat exchange is carried out with the mixture of raw materials and dilution steam to compensate for the decrease in total heat in the convection section after the reduction of flue gas volume, and to ensure that the mixture of raw materials and dilution steam reaches the set temperature for the pyrolysis reaction to occur in the radiation section.

[0154] 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. A pyrolysis method for utilizing waste heat from a pyrolysis furnace in stages, characterized in that, The raw material stream and dilution steam stream are fed into the convection section of the pyrolysis furnace for heating and mixing, and then fed into the radiation section of the pyrolysis furnace for pyrolysis reaction to obtain pyrolysis gas. The pyrolysis gas is subjected to multiple rapid cooling processes using dilution steam streams and / or combustion materials in the radiant section, thereby recovering the heat from the pyrolysis gas in stages.

2. The pyrolysis method according to claim 1, characterized in that, The combustion materials in the radiant section include fuel gas and air. In the presence of air, the fuel gas is burned in the radiant section to produce flue gas. The flue gas rises along the convection section to the top of the furnace, where it exchanges heat with the air before entering the radiant section and the flue gas at the top of the furnace; and / or The multiple rapid cooling processes utilize heat exchange media for heat exchange.

3. The pyrolysis method according to claim 2, characterized in that, The heat exchange medium is selected from molten salt and / or heat transfer oil; and / or Thermal oil is used as the heat exchange medium to exchange heat with the flue gas at 100-340℃ from the furnace top, and then with the air before it enters the radiation section.

4. The pyrolysis method according to claim 3, characterized in that, The molten salt is selected from one or more of chlorides, nitrates, fluorides, and carbonates; and / or The heat transfer oil is selected from at least one of alkylnaphthalene type, biphenyl and diphenyl ether low-melting-point mixture type, alkyl diphenyl ether type heat transfer oil or mineral type heat transfer oil; and / or The molten salt exchanges heat with the pyrolysis gas at 300-1200°C during repeated rapid cooling; and / or The heat transfer oil exchanges heat with the pyrolysis gas, which is below 340°C during multiple rapid cooling processes.

5. The pyrolysis method according to claim 4, characterized in that, The chloride salt includes lithium chloride and / or potassium chloride; and / or The nitrate is selected from at least one of sodium nitrate, sodium nitrite, or potassium nitrate; and / or The fluoride salt is selected from at least one of lithium fluoride, beryllium fluoride, or thorium fluoride; and / or The carbonate is selected from sodium carbonate and / or potassium carbonate.

6. The pyrolysis method according to claim 1, characterized in that, In the pyrolysis method, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling in sequence, wherein... A rapid cooling process allows the pyrolysis gas to exchange heat with the steam drum stream; The secondary quenching allows the cracked gas after the first quenching to exchange heat with the dilution steam stream; The three rapid cooling processes allow the cracked gas after the second rapid cooling to exchange heat with the air before entering the radiation section.

7. The pyrolysis method according to claim 1, characterized in that, In the pyrolysis method, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling in sequence, wherein... A rapid cooling process allows the pyrolysis gas to exchange heat with the air before entering the radiation section. Secondary quenching allows the cracked gas from the first quenching to exchange heat with the steam drum stream; The three rapid cooling processes allow the pyrolysis gas after the second rapid cooling to exchange heat with the boiler feedwater stream.

8. The pyrolysis method according to claim 7, characterized in that, The heat exchange in the rapid cooling process uses a heat exchange medium that first exchanges heat with the cracked gas, and then with the air before it enters the radiation section; and / or The heat exchange in the first rapid cooling process uses a heat exchange medium that first exchanges heat with the cracked gas, and then exchanges heat with the mixture of feedstock and dilution steam before exchanging heat with the air entering the radiation section; and / or The boiler feedwater first exchanges heat with the economizer and then with the cracked gas after secondary rapid cooling.

9. The pyrolysis method according to claim 1, characterized in that, In the pyrolysis method, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling in sequence, wherein... A rapid cooling process allows the pyrolysis gas to exchange heat with the air before entering the radiation section. Secondary quenching allows the cracked gas from the first quenching to exchange heat with the steam drum stream; The three rapid cooling processes allow the cracked gas after the second rapid cooling to exchange heat with the air before entering the radiation section.

10. The pyrolysis method according to claim 9, characterized in that, The heat exchange in the rapid cooling process uses a heat exchange medium that first exchanges heat with the cracked gas, and then with the air before it enters the radiation section; and / or The heat exchange in the first rapid cooling process uses a heat exchange medium that first exchanges heat with the cracked gas, and then exchanges heat with the mixture of feedstock and dilution steam before exchanging heat with the air entering the radiation section; and / or Before exchanging heat with the air before entering the radiation section, it first exchanges heat with a waste heat absorption medium, which is heat-conducting oil and / or molten salt.

11. The pyrolysis method according to any one of claims 5-10, characterized in that, The high-pressure steam stream generated by the steam drum is fed into the convection section of the pyrolysis furnace for superheating and then exchanges heat with the high-pressure boiler feedwater stream generated by the steam drum; afterwards, the high-pressure steam stream is fed back into the convection section of the pyrolysis furnace for superheating.

12. The pyrolysis method according to claim 1, characterized in that, In the pyrolysis method, when the amount of flue gas produced by the pyrolysis reaction is less than 500 Am. 3 At a rate of / h, the pyrolysis gas is subjected to a first rapid cooling, a second rapid cooling, and a third rapid cooling sequentially, wherein... A rapid cooling process allows the pyrolysis gas to exchange heat with the air before entering the radiation section. Secondary quenching involves cooling and regulating the temperature of the pyrolysis gas after the first quenching. The three rapid cooling processes allow the cracked gas after the second rapid cooling to exchange heat with the air before entering the radiation section.

13. The pyrolysis method according to claim 12, characterized in that, The heat exchange for rapid cooling uses a heat exchange medium, which first exchanges heat with the cracked gas and then with the air before entering the radiation section. and / or The heat exchange in the first rapid cooling process uses a heat exchange medium that first exchanges heat with the cracked gas, and then exchanges heat with the mixture of feedstock and dilution steam before exchanging heat with the air entering the radiation section; and / or It exchanges heat with the residual heat absorption medium before exchanging heat with the air before entering the radiation section; and / or The temperature control is to reduce the temperature of the pyrolysis gas after the secondary rapid cooling to below 300°C.

14. A pyrolysis apparatus, characterized in that, The pyrolysis device includes: The pyrolysis furnace includes a convection section and a radiation section, wherein the convection section is used to heat and mix the raw material stream (1) and the dilution steam stream (5) and send them into the radiation section for pyrolysis reaction to obtain pyrolysis gas stream (10); The quencher includes a first quencher (K), a second quencher (L) and a third quencher (O) connected in series through a cracked gas pipeline. The quencher is used to quench the cracked gas stream (10) multiple times and recover the heat of the cracked gas stream (10) in stages. A preheater, connected to the shell side of the quencher, is used to preheat and dilute the cracked gas dilution steam stream (5) and / or the air stream (22) before entering the radiation section.

15. The pyrolysis apparatus according to claim 14, characterized in that, The preheater includes a raw material and / or dilution steam preheater (T) and an air preheater (S); The top of the pyrolysis furnace is provided with a flue gas heat exchange section (P) connected to an air preheater (S), and the outlet of the air preheater (S) is connected to the inlet of the radiation section through a heat exchange medium pipeline.

16. The pyrolysis apparatus according to claim 14, characterized in that, The steam drum (N) and the shell side of the first quench cooler (K) form a circulation loop; The shell side of the second quench cooler (L) is connected in series with the dilution steam preheating section (F) on the dilution steam feed line; The third quencher (O) is connected to the air preheater (S) via a heat exchange medium pipeline.

17. The pyrolysis apparatus according to claim 14, characterized in that, The first quench cooler (K) is connected to the air preheater (S) via a heat exchange medium pipeline; The steam drum (N) and the shell side of the second quencher (L) form a circulation loop; The third quencher (O) is connected to the steam drum (N) via a boiler feedwater pipeline.

18. The pyrolysis apparatus according to claim 17, characterized in that, A raw material and / or dilution steam preheater (T) is provided on the heat exchange medium pipeline between the first quench cooler (K) and the air preheater (S); and / or The boiler feedwater flow pipeline passes through the economizer section (C).

19. The pyrolysis apparatus according to claim 14, characterized in that, The first quench cooler (K) is connected to the air preheater (S) via a heat exchange medium pipeline; The steam drum (N) and the shell side of the second quencher (L) form a circulation loop; The third quencher (O) is connected to the air preheater (S) via a heat exchange medium pipeline.

20. The pyrolysis apparatus according to claim 19, characterized in that, A raw material and / or dilution steam preheater (T) is provided on the heat exchange medium pipeline between the first quench cooler (K) and the air preheater (S); and / or A waste heat recovery heat exchanger (U) is provided on the heat exchange medium pipeline between the raw material and / or dilution steam preheater (T) and the air preheater (S); and / or A waste heat recovery heat exchanger (U) is installed on the heat exchange medium pipeline between the air preheater (S) and the third quencher (O).

21. The pyrolysis apparatus according to any one of claims 16-20, characterized in that, The discharge end of the steam drum (N) is connected to the feed end of the high-pressure steam superheating section i (G). The discharge end of the high-pressure steam superheating section i (G) is connected to the feed end of the high-pressure steam superheating section ii (H) through a pipeline equipped with a desuperheater (J). The feed end of the desuperheater (J) is connected to the high-pressure boiler feed water pipe. The discharge end of the high-pressure steam superheating section ii (H) is equipped with a high-pressure steam discharge pipe.

22. The pyrolysis apparatus according to claim 14, characterized in that, The first quench cooler (K) is connected to the air preheater (S) via a heat exchange medium pipeline; The third quencher (O) is connected to the air preheater (S) via a heat exchange medium pipeline.

23. The pyrolysis apparatus according to claim 22, characterized in that, A raw material and / or dilution steam preheater (T) is provided on the heat exchange medium pipeline between the first quench cooler (K) and the air preheater (S); and / or A waste heat recovery heat exchanger (U) is provided on the heat exchange medium pipeline between the raw material and / or dilution steam preheater (T) and the air preheater (S); and / or A waste heat recovery heat exchanger (U) is installed on the heat exchange medium pipeline between the air preheater (S) and the third quencher (O).

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