Burning method of steam cracking furnace

Abstract

The invention relates to a scorching method of a steam cracking furnace. The scorching method of the steam cracking furnace comprises the following steps: 1) carrying out gas-liquid separation on heavy hydrocarbon in a gas-liquid separation device to obtain a gas-phase material and a liquid-phase material, and depositing residues on the inner wall of the gas-liquid separation device, 2) conveying the gas-phase material to a radiation section furnace tube of the steam cracking furnace for pyrolysis, generating a pyrolysis product containing ethylene and depositing coke on the inner wall of the radiant section furnace tube; 3) conveying air and / or steam to pass through the radiation section furnace tube to remove at least a part of the coke to obtain scorched tail gas, and 4) enabling the scorched tail gas to enter a hearth of the steam cracking furnace through at least one combustor arranged in the hearth for combustion treatment. The decoking problem of the gas-liquid separation device of the heavy hydrocarbon cracking furnace can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of steam cracking, and more particularly to a coking method of a steam cracking furnace. Background Art

[0002] With the development of economy, the demand for hydrocarbon chemical raw materials is increasing day by day. As an important chemical raw material, the application market of ethylene is also expanding. Hydrocarbon cracking to produce ethylene is the mainstream process for producing ethylene in the current market.

[0003] During the operation of the cracking furnace, when hydrocarbons are thermally cracked at high temperature, catalytic coking, free radical coking and condensation coking will occur on the inner surface of the radiation section tube of the cracking furnace, and secondary reaction coking and condensation coking will occur on the inner surface of the quench heat exchanger. The coke produced adheres to the inner wall of the radiation section tube and the quench heat exchanger. The coke will increase the heat transfer resistance, increase the wall temperature of the radiation section tube, and increase the cracking gas temperature at the outlet of the quench heat exchanger. Therefore, in order to avoid overheating, it is necessary to regularly burn the coke produced by the radiation section tube. The burnt tail gas produced by the burnt treatment includes carbon oxides, water vapor and remaining coke particles. The temperature of the burnt tail gas of the cracking furnace is relatively high, generally in the range of 200-500℃.

[0004] For cracking furnaces containing high-boiling-point heavy hydrocarbon raw materials, the currently disclosed method is to first preheat the raw materials, then separate the materials that are not suitable for cracking through a gas-liquid separation device, and send the materials suitable for cracking to the cracking furnace for cracking. In this process, the gas-liquid separation system is also prone to produce residual oil and coke, causing a large pressure drop resistance, affecting the normal operation of the cracking furnace.

[0005] At present, there are two main destinations of the coke tail gas disclosed in conventional raw material cracking furnaces: Option 1 is to separate the coke particles through the coke cleaning tank and then discharge them into the atmosphere; Option 2 is to return to the coke burning port set separately at the bottom of the furnace for combustion, such as Figure 1 As shown. The inventors of the present invention found that it is difficult for Scheme 1 to meet environmental protection requirements only through simple physical separation. The inventors of the present invention also found that Scheme 2 will cause incomplete combustion of coke particles due to incomplete combustion of the coke gas in the furnace, which will accumulate at the bottom of the furnace. Some coke particles will be brought into the convection section, causing ash accumulation in the convection section, which will deteriorate the heat transfer effect. At the same time, due to the limited space at the bottom of the furnace, the newly added coke port can only be arranged between the burner and the furnace tube, and there is an impact of the return furnace steam on the radiation furnace tube, such as scouring, damage to the furnace tube caused by the return furnace steam carrying water, and the large diameter of the branch line, which makes it difficult to arrange the return furnace burning pipeline. The prior art has a small number of return furnace burning gas ports, uneven furnace temperature, and poor coking effect.

[0006] For a heavy hydrocarbon raw material cracking furnace, CN102227488B discloses a method for decoking a gas-liquid separation device, in which a mixture of steam and air is passed into the gas-liquid separation device for incineration, and the coke residue after incineration is passed through a decoking circulation pipe between the burners of the cracking furnace and returned to the furnace. Summary of the invention

[0007] The purpose of the present invention is to propose a new comprehensive treatment system and method for the burnt tail gas of a wide-fraction heavy hydrocarbon cracking furnace in view of the characteristics of cracking and returning to the furnace for burning in a wide-fraction heavy hydrocarbon cracking furnace.

[0008] According to a first aspect of the present invention, a method for charring in a steam cracking furnace is provided, comprising the following steps: 1) subjecting heavy hydrocarbons to gas-liquid separation in a gas-liquid separation device to obtain gas phase material and liquid phase material, and depositing residue on the inner wall of the gas-liquid separation device; 2) conveying the gas phase material to a radiant section furnace tube of a steam cracking furnace for pyrolysis to produce a pyrolysis product containing ethylene and depositing coke on the inner wall of the radiant section furnace tube; 3) conveying air and / or steam through the radiant section furnace tube to remove at least a portion of the coke to obtain charred tail gas; and 4) allowing the charred tail gas to enter the furnace of the steam cracking furnace through at least one burner arranged in the furnace for combustion treatment.

[0009] According to a preferred embodiment of the present invention, the charring method further includes the following steps: A) conveying steam through the gas-liquid separation device to remove at least a portion of the residue to obtain mixed steam, and B) conveying the mixed steam through the radiation section furnace tube to remove at least a portion of the coke to obtain the charring tail gas.

[0010] Technical Effects

[0011] 1. The inventors of the present invention have found that the coke produced in the furnace tube during the operation of the heavy hydrocarbon cracking furnace is looser than the coke produced by conventional gas or light liquid raw materials. Therefore, when the coke particles return to the furnace with the coke gas, they do not need to return to the furnace through a larger coke port, but can be returned to the burner through a specially designed coke nozzle. The coke particles are loose in texture and therefore not easy to cause burner blockage. Returning to the burner solves the problem of separate airflow impact during the operation of coke gas returning to the furnace in the existing cracking furnace, which has a negative impact on the furnace thermal field, burner combustion, and negative pressure fluctuations, reduces the fluctuation problem of the operating conditions, makes the coke gas more evenly distributed in the furnace, and significantly improves the furnace temperature distribution, thereby ensuring that the heating conditions of different groups of radiation furnace tubes in the furnace are consistent, and greatly improves the coking effect in the furnace tube.

[0012] 2. The present invention aims at the characteristic that the heavy hydrocarbon cracking furnace process contains a unique gas-liquid separation device. Before the coking operation, the cracking furnace and the gas-liquid separation device are steam-purged. Before the coking operation, the steam carries the residual hydrocarbons evaporated from the gas-liquid separator into the radiation section furnace tube. The volatile hydrocarbons contained in the mixed steam are helpful to loosen and remove the coke on the furnace tube, thereby improving the coke cleaning effect in the furnace tube during coking.

[0013] 3. The system of the present invention can effectively solve the decoking problem of the gas-liquid separation device of the heavy hydrocarbon cracking furnace, avoid the safety risk of direct contact between the charred air and the hydrocarbon, and prevent equipment damage. In addition, the system is easy to switch, and there is no need to empty the gas-liquid separation system, which reduces the operating workload and avoids safety hazards caused by misoperation.

[0014] 4. The present invention can reduce the flame temperature of combustion and the concentration of oxygen by introducing the burnt tail gas into the burner, thereby effectively reducing the amount of NOx generated by combustion.

[0015] 5. Since the branch pipelines of the return furnace pipeline are provided in the same number as the burners, the branch pipelines are connected to the special nozzles for burnt tail gas provided in the burners. Compared with the prior art (Scheme 2) in which a burnt port is provided separately at the bottom of the furnace, the branch pipelines of the return furnace pipeline provided in the present invention are small in size and occupy a small space, thus solving the problem of difficult arrangement of the return furnace burnt port and pipelines. Moreover, since the burnt port is far away from the furnace tube, the furnace tube is avoided from being flushed or damaged by water carried by the return furnace steam.

[0016] 6. When the charred gas passes through the burner, due to the limited size of the charred gas nozzle, there is a certain throttling effect, which can reduce the uneven flow / flow velocity of each charred port caused by uneven pipeline distribution, thereby avoiding the charred gas returning to the furnace due to uneven pressure in the furnace, and the high-temperature flue gas in the local space / pipeline is mixed, causing pipeline overheating, combustion disorder, etc.

[0017] 7. It has a better combustion effect on the particles in the charred gas, which can reduce the requirements for the charred tank. At present, the charred tank must reach 20mg / Nm 3 The emission requirements are more difficult to meet. The main function of the charring tank is to separate the larger particles into cyclones. If they are directly returned to the furnace, for example, 50mg / Nm 3 Since the particles in the furnace are not in direct contact with the burning flame, the combustion effect is poor, which will cause the particles at the chimney outlet of the cracking furnace to exceed the standard (ultimately exceeding 20mg / Nm 3 The burner can improve the effect of particle burning, which can reduce the requirements for the burning tank on the one hand, and prevent the unburned particles from being carried to the convection section to cause ash accumulation on the fins or remaining at the bottom of the furnace, affecting the flue gas circulation on the other hand.

[0018] 8. For the cracking of wide-fraction crude oil, the coke formed by the cracking reaction has different characteristics from the coke formed by the cracking of conventional raw materials (ethane, LPG, NAP, etc.). The distillation range of the light component of crude oil is wider, and the particle diameter of the coke formed is larger, looser, and has a lower hardness. The cyclone effect in the coke cleaning tank is better for particles with larger particle diameters. Most of the larger particles are captured in the coke cleaning tank, which can prevent the larger particles from returning to the burner and clogging the burner nozzle and the coke nozzle returning to the furnace. However, the coke particles formed by the cracking of conventional raw materials are directly smaller in distribution, and the separation effect in the coke cleaning tank is poor. There will be more small particles of coke returning to the furnace with the coke gas, so they cannot be directly introduced into the burner, and clog the burner nozzle and the coke gas nozzle. According to the characteristics of coke produced by direct cracking of crude oil and the characteristics of coke particles in the furnace, the present invention proposes a new idea to improve the coking effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The overall schematic diagram of the solution 2 mentioned in the background technology of the present invention, in which a charring port is separately arranged at the bottom of the return furnace, is shown.

[0020] Figure 2 A detailed schematic diagram showing a separate charring port at the bottom of the return furnace of solution 2 mentioned in the background of the present invention is shown.

[0021] Figure 3 The schematic diagram of the subsequent connection structure of the burnt tail gas pipeline of the comprehensive treatment system of the burnt tail gas of the heavy hydrocarbon cracking furnace of the present invention is shown.

[0022] Figure 4 The schematic diagram of the subsequent connection structure of the burnt tail gas pipeline of the comprehensive treatment system of the burnt tail gas of the heavy hydrocarbon cracking furnace of the present invention is shown.

[0023] Figure 5 A top view of a subsequent connection structure of a burnt tail gas pipeline of a comprehensive treatment system for burnt tail gas from a heavy hydrocarbon cracking furnace of the present invention is shown.

[0024] Figure 6 A schematic diagram of a burner of a comprehensive treatment system for charred tail gas from a heavy hydrocarbon cracking furnace provided by the present invention is shown.

[0025] Figure 7 A schematic diagram of a comprehensive treatment system for charred tail gas from a heavy hydrocarbon cracking furnace provided by the present invention is shown.

[0026] The following are the descriptions of the reference numerals:

[0027] 1-burning tail gas pipeline, 2-decoking tank, 3-main pipeline, 4.1-bottom burner,

[0028] 4.2- side wall burner, 5- furnace of the radiant section of the cracking furnace, 6- branch pipe line, 7- charring port of the return furnace;

[0029] 8-quench heat exchanger, 10-upper heavy hydrocarbon preheating section, 11-primary dilution steam superheating section, 12-secondary dilution steam superheating section, 13-lower superheating section, 14-gas-liquid separation device, 15-cracking furnace radiation section;

[0030] 16-heavy hydrocarbon feed pipeline, 17-air feed pipeline, A-first valve, B-second valve, 18-inlet of gas-liquid separation device, 19-gas phase outlet of gas-liquid separation device, 20-liquid phase outlet of gas-liquid separation device, 21-primary dilution steam feed pipeline, 22-secondary dilution steam feed pipeline, 23-burnt tail gas, 24-cracking gas. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are described in detail below, but it should be pointed out that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the claims in the appendix.

[0032] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definitions in this specification shall prevail.

[0033] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0034] In the context of the present invention, all numerical values ​​for parameters (eg amounts or conditions) are to be understood as being modified in all instances by the term "about", regardless of whether "about" actually appears before the numerical value.

[0035] In the context of the present invention, “substantially” means that deviations that are acceptable or reasonable to those skilled in the art are allowed to exist, such as deviations within ±2%, ±1%, ±0.5% or ±0.1%.

[0036] In the context of the present invention, the terms "primary dilution steam", "secondary dilution steam" and the like are used only to distinguish the steam introduced in different steps, but do not contain any actual meaning such as the properties of the steam itself.

[0037] In the context of the present invention, unless otherwise specified, each device used in the present invention may use a structure conventionally selected in the art without any particular limitation.

[0038] In the context of the present invention, heavy hydrocarbons refer to mixed hydrocarbons with a wide fraction, and their final boiling point is generally above 540°C, such as an initial boiling point temperature of 15°C and a final boiling point temperature of about 750°C. In particular, the heavy hydrocarbons can be selected from one or more of the following raw materials: paraffin-based crude oil, intermediate-based crude oil, naphthenic crude oil, condensate oil and refined products, etc. Here, as refined products, for example, gasoline, kerosene, diesel, tail oil, fuel oil, reformed oil, etc. processed by refineries such as atmospheric and vacuum, reforming, catalytic, coking and other refining units can be cited.

[0039] In the context of the present invention, the measurement method of the initial distillation point, the final distillation point and the distillation range is the atmospheric and vacuum distillation of crude oil, wherein the atmospheric distillation analysis method adopts ASTM D-2892, and the vacuum distillation analysis method adopts ASTM D-5236.

[0040] In the context of the present invention, API refers to specific gravity index, and its analysis method adopts ASTM D-2320.

[0041] In the context of the present invention, the method for measuring the solid particle content is a light scattering method.

[0042] In the context of the present invention, the method of measuring the average particle size is laser light scattering.

[0043] In the context of the present invention, the gasification rate refers to the mass percentage of the gas phase material (excluding steam) to the total amount of feed (excluding steam).

[0044] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight and pressure is gauge pressure.

[0045] In the context of the present invention, any two or more embodiments or aspects of the present invention may be arbitrarily combined, and the technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0046] According to one embodiment of the present invention, a coking method for a steam cracking furnace is disclosed.

[0047] During the operation of the cracking furnace, when hydrocarbons are thermally cracked at high temperature, catalytic coking, free radical coking and condensation coking will occur on the inner surface of the radiation section furnace tube of the cracking furnace, and secondary reaction coking and condensation coking will occur on the inner surface of the quench heat exchanger. The produced coke adheres to the inner wall of the radiation section furnace tube and the quench heat exchanger. The coke will increase the heat transfer resistance, increase the wall temperature of the radiation section furnace tube, and increase the cracking gas temperature at the outlet of the quench heat exchanger. Therefore, in order to avoid overheating, it is necessary to regularly burn the coke produced by the radiation section furnace tube, etc.

[0048] According to one embodiment of the present invention, the coking method includes step 1): subjecting heavy hydrocarbons to gas-liquid separation in a gas-liquid separation device to obtain gas phase materials and liquid phase materials, and depositing residues on the inner wall of the gas-liquid separation device. The inventors of the present invention have found that the main component of the residue is carbon, including coke and volatile hydrocarbons, wherein the hydrogen content of the coke is relatively low, and it also contains a small amount of sulfur, nitrogen and inorganic salt components. Microscopically, the coke is composed of countless tiny spherical particles of different diameters. Since the gas-liquid separation device itself has a large flow area, some of the residual volatile hydrocarbons in the gas-liquid separation device will follow the steam purge to the radiation section furnace tube. The volatile hydrocarbons brought in by the gas-liquid separator cause the coke layer deposited on the furnace tube to loosen and dissolve, which is helpful for the subsequent coking and removal of coke from the furnace tube.

[0049] According to one embodiment of the present invention, the final distillation temperature of the heavy hydrocarbon is above 540°C (preferably the initial distillation temperature is 15°C and the final distillation temperature is above 750°C). Preferably, the API value of the heavy hydrocarbon is not less than 32 (preferably above 38). As an example, the heavy hydrocarbon is selected from at least one of paraffinic crude oil, intermediate crude oil, naphthenic crude oil, condensate oil and refined products.

[0050] According to one embodiment of the present invention, the heavy hydrocarbons are heated to a temperature of 100-400° C. (preferably 200-370° C.) before the gas-liquid separation. According to the present invention, the heating can be carried out in any manner conventionally known in the art, but is generally achieved in the convection section of the cracking furnace.

[0051] According to one embodiment of the present invention, the gas-liquid separation device is not particularly limited, and can be any type of gas-liquid separation device conventionally known in the art. In addition, the present invention does not particularly limit the operating conditions of the gas-liquid separation, but as an example, the operating temperature of the gas-liquid separation is generally 260-360°C, the operating pressure is generally 0.2-0.7MPaG, and the gasification rate is generally 50-80%.

[0052] According to one embodiment of the present invention, the coking method comprises step 2): transporting the gaseous material to the radiant section furnace tube of the steam cracking furnace for pyrolysis to produce a pyrolysis product containing ethylene and depositing coke on the inner wall of the radiant section furnace tube. The inventor of the present invention found that filamentous coke will be formed on the furnace tube due to catalytic coking, and tar droplets or coke particles will be formed by free radical coking or gas phase coking and uniformly adhere to the surface of the furnace tube, and finally enter a stable coking layer, and the coking layer becomes thicker as the operating time increases. Coking will increase the heat transfer resistance of the cracking furnace tube wall, reduce the heat transfer coefficient, cause the temperature of the outer wall of the furnace tube to rise, and cause local overheating, which will shorten the service life of the furnace tube.

[0053] According to the present invention, there is no limitation on the specific structure of the cracking furnace and the radiant section furnace tube, and the operating conditions of the pyrolysis, and the conventional contents in the field of steam cracking technology can be directly applied. For example, the operating temperature of the pyrolysis is generally 800-900°C, and the operating pressure is generally 0.06-0.15MPaG.

[0054] According to one embodiment of the present invention, the coking method comprises step 3): air and / or steam are conveyed through the radiation section furnace tube to remove at least a portion of the coke (referred to as coking scheme 1) to obtain coking tail gas. Here, the air and the steam can be used separately or in combination. When used in combination, the ratio of the air and the steam can be selected according to the numerical range conventionally known in the art, and is not particularly limited.

[0055] According to one embodiment of the present invention, the pyrolysis product is cooled, preferably cooled to 400-600°C through a quench heat exchanger. According to the present invention, since the pyrolysis product is transported through the quench heat exchanger, coke deposition also occurs in the quench heat exchanger. To this end, the charring method of the present invention also includes a process of charring the quench heat exchanger, such as by step 3), allowing air and / or steam to be transported through the radiation section furnace tube and the quench heat exchanger in sequence to remove at least a portion of the coke (referred to as charring scheme 2), thereby obtaining the charring tail gas.

[0056] According to one embodiment of the present invention, in step 3), for the purpose of the charring, the temperature of the air is 500-650°C, the pressure is 0.2-0.4MPaG, and the inlet linear velocity is 30-80m / s. In addition, for the purpose of the charring, the temperature of the steam is 500-650°C, the pressure is 0.2-0.4MPaG, and the inlet linear velocity is 30-80m / s. According to the present invention, the air and the steam can reach these operating conditions by any conventional means known in the art, such as heating to the required temperature, especially through the convection section of the cracking furnace or a separately arranged preheater, etc., and there is no special limitation. In addition, the so-called inlet linear velocity refers to the linear velocity of the air or steam at the inlet of the radiation section furnace tube. The inventors of the present invention have found that if the temperature of the air or steam is too low, the starting temperature of the charring reaction cannot be reached, the charring effect cannot be achieved, the charring time is prolonged, and more fuel is consumed. If the temperature of the air or steam is too high, it is easy to cause local hot spots, causing overheating damage to the furnace tube. The inventors of the present invention also found that if the inlet linear velocity of the air or steam is too low, the distribution of the air or steam in different groups of furnace tubes will be uneven, resulting in temperature deviations between the furnace tubes and causing some furnace tubes to overheat. If the inlet linear velocity of the air or steam is too high, the pressure drop in the furnace tubes will be too large, the overall operating costs of the system will increase significantly, and it will also cause furnace tube deviation.

[0057] According to one embodiment of the present invention, before step 3) starts, the gas phase material is stopped from being transported to the radiant section furnace tube, i.e., the operation of step 2) is stopped. To this end, according to this embodiment of the present invention, pyrolysis and charring are two steps that are performed independently of each other and are not performed simultaneously.

[0058] According to one embodiment of the present invention, the charring method further comprises step A): conveying steam through the gas-liquid separation device to remove at least a portion of the residue to obtain mixed steam. The inventors of the present invention have found that if air is conveyed to the gas-liquid separation device, the air and the residual hydrocarbons in the gas-liquid separation device will explode, posing a safety hazard. The inventors of the present invention have also found that by conveying steam to the gas-liquid separation device and utilizing the purge effect of the steam, at least a portion of the residue (mainly volatile hydrocarbons) is vaporized and entrained by the steam, thereby forming a mixture of the steam and the volatile hydrocarbons, i.e., the mixed steam.

[0059] According to one embodiment of the present invention, the temperature of the steam is 500-650°C, the pressure is 0.2-0.4MPaG, and the inlet linear velocity is 30-80m / s. Here, the so-called inlet linear velocity refers to the linear velocity of the steam at the steam inlet of the gas-liquid separation device. The inventors of the present invention found that if the temperature of the steam is too low, the steam purging effect becomes worse, the purging time is increased, and the operating costs are increased. If the temperature of the steam is too high, it will cause local overheating of the equipment, posing a safety hazard. The inventors of the present invention also found that if the inlet linear velocity of the steam is too low, the purging effect becomes worse, and the oil stored in the pipelines before and after the gas-liquid separator cannot be effectively removed. If the inlet linear velocity of the steam is too high, the system pressure drop is too large, increasing the operating costs. At the same time, too fast a flow rate will cause pipeline vibration, which is easy to cause safety hazards.

[0060] According to one embodiment of the present invention, the temperature of the mixed steam is 250-400°C, the pressure is 0.2-0.4MPaG, and the outlet linear velocity is 25-40m / s. Here, the so-called outlet linear velocity refers to the linear velocity of the mixed steam leaving the mixed steam outlet of the gas-liquid separation device or the linear velocity of the mixed steam at the inlet of the radiation section furnace tube. The inventors of the present invention have found that if the temperature of the mixed steam is too low, the temperature of the mixed steam entering the radiation section is low, which affects the charring effect of the furnace tube, and if the temperature of the mixed steam is too high, it is easy to cause overheating of the pipeline or equipment. The inventors of the present invention have also found that if the outlet linear velocity of the mixed steam is too low, it affects the uniformity of the mixed steam distribution in the furnace tube, and if the outlet linear velocity of the mixed steam is too high, it will cause excessive pressure drop in the system and increase operating costs.

[0061] According to one embodiment of the present invention, the coking method further includes step B): transporting the mixed steam through the radiation section furnace tube to remove at least a portion of the coke (referred to as coking scheme three) to obtain the coking tail gas. As mentioned above, the inventors of the present invention have found that since the mixed steam contains volatile hydrocarbons, the volatile hydrocarbons contain some hydrocarbons with a final distillation point above 540°C and residues remaining on the gas-liquid separator, and the main component of the residue is carbon, including coke and volatile hydrocarbons, wherein the hydrogen content of the coke is relatively low, and it also contains a small amount of sulfur, nitrogen and inorganic salt components. Microscopically, the coke is composed of countless tiny spherical particles of different diameters. Since the gas-liquid separation device itself has a large flow area, some of the residual volatile hydrocarbons in the gas-liquid separation device will follow the steam to blow to the radiation section furnace tube. The volatile hydrocarbons brought in by the gas-liquid separator cause the coke layer deposited on the furnace tube to loosen and dissolve, which is helpful for the subsequent coking and removal of coke in the furnace tube.

[0062] According to one embodiment of the present invention, before step A) starts, the heavy hydrocarbons are stopped from being transported to the gas-liquid separation device, i.e., the operation of step 1) is stopped. To this end, according to this embodiment of the present invention, gas-liquid separation and charring are two steps that are performed independently of each other and are not performed simultaneously.

[0063] According to one embodiment of the present invention, after step B) is completed, step 3) is started, that is, first the mixed steam is conveyed through the radiation section furnace tube to remove at least a portion of the coke (referred to as coking scheme four) to obtain burnt tail gas, and then air or a mixture of steam and air is conveyed through the radiation section furnace tube to remove at least a portion of the coke to obtain burnt tail gas. The inventors of the present invention have discovered that in order to effectively prevent air from entering the gas-liquid separation device, step B) and step 3) cannot be performed simultaneously, but must be performed one after the other. Steam blowing must be performed first to clean the residual hydrocarbons in the convection section furnace tube and pipeline, and after the gas-liquid separator is cut out of the system, air can be introduced. Otherwise, the air will encounter the residual hydrocarbons in the pipeline that have not been cleaned out, which will cause explosion and bring safety hazards.

[0064] According to one embodiment of the present invention, the charring method comprises step 4): allowing the charring tail gas to enter the furnace of the steam cracking furnace through at least one burner (referred to as a charring burner) arranged in the furnace for combustion treatment. In the context of the present invention, any tail gas obtained by charring is collectively referred to as charring tail gas, without distinguishing the specific charring scheme.

[0065] According to one embodiment of the present invention, there is no particular limitation on the operating conditions of the combustion treatment, and the conventionally known contents in the art can be directly applied, but as an example, the operating temperature between the char gas return burners is 300-400°C, and the operating pressure is 0.01-0.1MPaG.

[0066] According to one embodiment of the present invention, there is no particular limitation on the structure of the char burner, as long as it is provided with a char exhaust gas channel so that the char exhaust gas enters the furnace through the char exhaust gas channel. Preferably, the char burner includes a central channel and one or more annular channels arranged around the central channel. More preferably, from the perspective of effectively preventing channel blockage and sufficient combustion, the central channel is a char exhaust gas channel, the annular channel arranged adjacent to the outer side of the central channel is an air channel, and the annular channel arranged adjacent to the outer side of the air channel is a fuel channel. The inventors of the present invention have found that a burner of this specific structure is particularly suitable for use as the char burner of the present invention.

[0067] According to one embodiment of the present invention, in step 4), the burnt tail gas is transported through the burnt tail gas main pipeline, and then transported to the burnt burner through a plurality of branch pipelines arranged on the burnt tail gas main pipeline. Generally speaking, the number of the branch pipelines is the same as the number of the burnt burners, thereby ensuring that one branch pipeline corresponds to one burnt burner. According to the present invention, depending on the specific burnt scheme, the burnt tail gas main pipeline can be connected to the outlet of the radiant section furnace tube, or can be connected to the outlet of the quench heat exchanger, without any special restrictions.

[0068] According to one embodiment of the present invention, in step 4), the char burner is arranged at the bottom and / or side wall of the furnace, preferably at the bottom and side wall of the furnace. In addition, according to the present invention, there is no particular limitation on the number of the char burners, but generally it is 20-100% of the total number of all burners arranged in the furnace, preferably 50-100% or 100%.

[0069] According to one embodiment of the present invention, the charred tail gas delivered to the charred burner arranged at the bottom of the furnace accounts for 50-100wt% (preferably 65-85wt%) of the total mass of the charred tail gas, and the charred tail gas delivered to the charred burner arranged at the side wall of the furnace accounts for 0-50wt% (preferably 15-35wt%) of the total mass of the charred tail gas. The inventors of the present invention have found that the load of the side wall burner usually accounts for 10%-30% of the total combustion load, so the amount of charred tail gas entering the side wall burner is equivalent to this load.

[0070] According to one embodiment of the present invention, in step 4), the total mass flow rate of the charred tail gas is 40 t / hr-120 t / h. At this time, the inner diameter of the charred tail gas main pipeline is generally 250-800 mm.

[0071] According to one embodiment of the present invention, in step 4), at least a portion of solid particles are separated from the charred tail gas to obtain purified tail gas, and then the purified tail gas enters the furnace through the at least one charred burner for the combustion treatment. According to the present invention, the separation can be carried out according to any gas-solid separation method conventionally known in the art, and there is no particular limitation. As an example, the separation is carried out in a coke cleaning tank (preferably a cyclone coke cleaning tank). At this time, the charred tail gas main pipeline can be connected to the outlet of the coke cleaning tank.

[0072] According to one embodiment of the present invention, the solid particle content of the purified tail gas is less than 50 mg / Nm 3 , preferably less than 20mg / Nm 3, based on the total weight of the purified tail gas being 100wt%. Preferably, the solid particles contained in the purified tail gas have an average particle size ranging from 1μm to 20mm (preferably less than 10mm). The inventors of the present invention have found that the present invention has a better combustion effect on particles in the char gas and can reduce the requirements for the char tank. At present, the char tank must reach a particle size of 20mg / Nm 3 The emission requirements are more difficult to meet. The main function of the charring tank is to separate the larger particles into cyclones. If they are directly returned to the furnace, for example, 50mg / Nm 3 Since the particles in the furnace are not in direct contact with the burning flame, the combustion effect is poor, which will cause the particles at the chimney outlet of the cracking furnace to exceed the standard (ultimately exceeding 20mg / Nm 3 The burner can improve the effect of particle burning, which can reduce the requirements for the burning tank on the one hand, and prevent the unburned particles from being carried to the convection section to cause ash accumulation on the fins or remaining at the bottom of the furnace, affecting the flue gas circulation.

[0073] The present invention is described in more detail below by taking a comprehensive treatment system for burnt tail gas from a heavy hydrocarbon cracking furnace as an example, but the present invention is not limited thereto.

[0074] According to one embodiment of the present invention, the comprehensive treatment system for burnt tail gas from a heavy hydrocarbon cracking furnace includes a cracking furnace convection section, a gas-liquid separation device, a first valve, a second valve, a cracking furnace radiation section, a burner, a quench heat exchanger, a burnt tail gas pipeline, a return furnace pipeline, and optionally a decoking tank.

[0075] According to one embodiment of the present invention, the convection section of the cracking furnace comprises at least an upper heavy hydrocarbon preheating section, a dilution steam superheating section and a lower superheating section; the inlet of the upper heavy hydrocarbon preheating section is connected to a heavy hydrocarbon feed pipeline; the inlet of the dilution steam superheating section is connected to a dilution steam feed pipeline, and optionally to an air feed pipeline; the outlet of the dilution steam superheating section is respectively connected to the first valve and the second valve; the first valve is connected to the inlet of the lower superheating section via the inlet of the gas-liquid separation device and the gas phase outlet of the gas-liquid separation device in sequence; the second valve is directly connected to the inlet of the lower superheating section.

[0076] According to one embodiment of the present invention, the outlet of the lower superheating section is connected to the inlet of the burnt tail gas at one end of the burnt tail gas pipeline through the cracking furnace radiation section and the quench heat exchanger in sequence.

[0077] According to one embodiment of the present invention, the other end of the burnt exhaust gas pipeline, the return furnace pipeline and the burner that introduces the burnt exhaust gas are connected in sequence, or the other end of the burnt exhaust gas pipeline, the coke cleaning tank, the return furnace pipeline and the burner that introduces the burnt exhaust gas are connected in sequence.

[0078] According to one embodiment of the present invention, there are multiple burners arranged at the bottom and / or side walls of the furnace of the radiation section of the cracking furnace.

[0079] According to one embodiment of the present invention, preferably, the dilution steam superheating section comprises a primary dilution steam superheating section and a secondary dilution steam superheating section; the inlet of the primary dilution steam superheating section is connected to a primary dilution steam feed pipeline, and optionally to an air feed pipeline; the inlet of the secondary dilution steam superheating section is connected to a secondary dilution steam feed pipeline.

[0080] According to one embodiment of the present invention, the outlet of the primary dilution steam superheating section is connected to the first valve and the second valve respectively.

[0081] According to one embodiment of the present invention, the outlet of the secondary dilution steam superheating section is connected to the first valve and the second valve respectively.

[0082] According to one embodiment of the present invention, the liquid phase outlet of the gas-liquid separation device is connected to the outside.

[0083] According to one embodiment of the present invention, the return furnace pipeline includes a plurality of main pipelines, and each main pipeline is divided into a plurality of branch pipelines.

[0084] According to one embodiment of the present invention, each burner into which the charred tail gas is introduced is correspondingly connected to a branch pipeline, and is connected to the main pipeline through the branch pipeline.

[0085] According to one embodiment of the present invention, the decoking tank is a cyclone type decoking tank.

[0086] According to one embodiment of the present invention, each burner into which the charred tail gas is introduced is provided with a plurality of nozzles, wherein at least one nozzle is only connected to the branch pipeline.

[0087] According to one embodiment of the present invention, the number of burners fed with the charred tail gas accounts for 20-100% of the total number of burners in the system, preferably 50-100%.

[0088] According to one embodiment of the present invention, the burner for introducing the charred tail gas is arranged at the bottom and / or side wall of the furnace of the radiation section of the cracking furnace.

[0089] According to the comprehensive treatment method of the heavy hydrocarbon cracking furnace charred tail gas of the present invention, the method adopts the system and comprises the following steps:

[0090] S1: sending steam into the convection section of the cracking furnace to heat it, obtaining heating steam and sending it into the gas-liquid separation device through the first valve, mixing the heating steam with the residual hydrocarbons in the gas-liquid separation device, obtaining a mixture, and sending it into the inlet of the lower superheating section through the gas phase outlet of the gas-liquid separation device; or,

[0091] Sending steam and optionally air into the convection section of the cracking furnace to heat it, obtaining heated gas and sending it into the inlet of the lower superheating section through the second valve;

[0092] S2: subjecting the mixture or the heated gas to heating in the lower superheating section and charring in the radiation section of the cracking furnace in sequence to obtain charred tail gas;

[0093] S3: sending the burnt tail gas to the burner arranged at the bottom and / or side wall of the furnace of the radiant section of the cracking furnace through the quench heat exchanger, the burnt tail gas pipeline and the furnace return pipeline in sequence for combustion treatment; or,

[0094] The burnt exhaust gas is sent to the decoking tank for treatment through the quench heat exchanger and the burnt exhaust gas pipeline, and then sent from the decoking tank through the return furnace pipeline to the burner arranged at the bottom and / or side wall of the furnace of the cracking furnace radiation section for combustion treatment.

[0095] According to one embodiment of the present invention, the residual hydrocarbons are residual oil and coke produced by gas-liquid separation of the heavy hydrocarbons.

[0096] According to one embodiment of the present invention, the final distillation point of the heavy hydrocarbon is above 540°C.

[0097] According to one embodiment of the present invention, the steam includes steam for primary dilution steam superheating section feed and / or steam for secondary dilution steam superheating section feed.

[0098] According to one embodiment of the present invention, the charring tail gas includes at least one of steam, carbon oxides, air and coke powder.

[0099] According to one embodiment of the present invention, the gas flow rate in the return furnace pipeline is 120-2500 kg / h, preferably 300-1000 kg / h.

[0100] According to one embodiment of the present invention, the mass flow rate of the burnt tail gas fed into the burner arranged at the bottom of the furnace of the radiant section of the cracking furnace is 50-100% of the total mass flow rate of the burnt tail gas, preferably 65%-85%; the mass flow rate of the burnt tail gas fed into the burner arranged at the side wall of the furnace of the radiant section of the cracking furnace is 0-50% of the total mass flow rate of the burnt tail gas, preferably 15%-35%. In the present invention, as a preferred embodiment, the gas flow rate in the branch line connected to each bottom burner is the same; the gas flow rate in the branch line connected to each side wall burner is the same.

[0101] The present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0102] According to the comprehensive treatment system of the pyrolysis furnace char tail gas of the present invention, Figure 3 As shown. The system includes a burnt tail gas pipeline 1, a return furnace pipeline, a burner, a cracking furnace radiation section furnace 5 and a de-coking tank 2; the de-coking furnace radiation section furnace 5 is a bottom + side wall combined heating system; one end of the burnt tail gas pipeline 1 is the inlet of the burnt tail gas; the other end of the burnt tail gas pipeline 1, the de-coking tank 2, the return furnace pipeline and the burner that introduces the burnt tail gas are connected in sequence; there are multiple burners that introduce the burnt tail gas. The return furnace pipeline includes multiple main pipelines 3, and each main pipeline 3 is divided into multiple branch pipelines 6; each burner that introduces the burnt tail gas is connected to a corresponding branch pipeline 6, and is connected to the main pipeline 3 through the branch pipeline 6. Each burner that introduces the burnt tail gas is provided with multiple nozzles, such as Figure 6 As shown, one of the nozzles is only connected to the branch line 6. The decoking tank 2 is a cyclone type decoking tank.

[0103] According to the present invention, the comprehensive treatment method of the charred tail gas of the cracking furnace using the above-mentioned system includes the following steps: the charred tail gas generated by the charred treatment of the cracking furnace is sent to the decoking tank 2 through the charred tail gas pipeline 1 for preliminary separation treatment, and then sent from the decoking tank 2 through the return furnace pipeline to the burner arranged at the bottom and side wall of the cracking furnace radiation section furnace 5 for combustion treatment.

[0104] According to another comprehensive treatment system of cracking furnace char tail gas of the present invention, Figure 4 , 5As shown, the system includes a burnt tail gas pipeline 1, a return furnace pipeline, a burner, and a cracking furnace radiation section furnace 5; the cracking furnace radiation section furnace 5 is the entire bottom heating system; one end of the burnt tail gas pipeline 1 is the inlet of the burnt tail gas; the other end of the burnt tail gas pipeline 1, the return furnace pipeline and the burner that introduces the burnt tail gas are connected in sequence; there are multiple burners that introduce the burnt tail gas. The return furnace pipeline includes multiple main pipelines 3, and each main pipeline 3 is divided into multiple branch pipelines 6; each burner is connected to a corresponding branch pipeline 6, and is connected to the main pipeline 3 through the branch pipeline 6. Each burner that introduces the burnt tail gas is provided with multiple nozzles, such as Figure 6 As shown, one of the nozzles is connected to only the branch line 6 .

[0105] According to the present invention, the comprehensive treatment method of cracking furnace burnt tail gas using the above system includes the following steps: the burnt tail gas generated by the cracking furnace burnt treatment is sent to the bottom burner 4.1 arranged in the cracking furnace radiation section furnace 5 through the burnt tail gas pipeline 1 and the return furnace pipeline in sequence for combustion treatment.

[0106] Example

[0107] The present invention is further described in detail below using examples and comparative examples, but the present invention is not limited to these examples.

[0108] The raw materials used in the examples and comparative examples were all obtained from commercial sources.

[0109] The comparison indicators in the embodiments and comparative examples are the duration of charring, the concentration of particulate matter in the flue gas, the NOx emission index in the flue gas, the deviation of the furnace tube outlet temperature (COT for short) during charring, the online operation time of the cracking furnace throughout the year, the equipment maintenance fee, the economic loss fee, etc.

[0110] The duration of the coking refers to the total time from the start of the coking to the end of the coking when the cracking furnace performs a single coking operation.

[0111] The method for measuring the NOx emission index in the flue gas is a chemiluminescence online monitoring method.

[0112] The furnace tube COT deviation during the coking period refers to the absolute value of the deviation of the outlet temperature of the radiation section furnace tube, and the detection means is a furnace tube surface thermometer.

[0113] The annual online operation time of the cracking furnace refers to the total time of the cracking furnace during the feeding operation period.

[0114] The equipment maintenance fee is based on the one-time equipment renewal purchase cost.

[0115] The economic loss fee is calculated based on the average market price of high value-added products in the past three years.

[0116] Example 1

[0117] Heavy hydrocarbon is used as a cracking furnace feed for steam cracking, and the heavy hydrocarbon is a wide-fraction crude oil, and a low-sulfur paraffin-based crude oil with an API value of 44 is used. The initial boiling point of the heavy hydrocarbon is 15°C, and the final boiling point is 800°C.

[0118] like Figure 7 As shown, the system comprises a cracking furnace, a gas-liquid separation device (14), a coke removal tank (2), and a quench heat exchanger (8). The cracking furnace comprises a heavy hydrocarbon preheating section (10), a mixed superheating upper section (11), a dilution steam superheating section (12), a mixed superheating lower section (13), a radiation section furnace tube (15), a primary dilution steam feed pipeline (21), a secondary dilution steam feed pipeline (22), and an air feed pipeline (17).

[0119] In the cracking furnace operation mode, the heavy hydrocarbon first enters the heavy hydrocarbon preheating section (10) at the top of the cracking furnace for preheating, and the feed rate of the heavy hydrocarbon is 100 t / h. The temperature of the preheated heavy hydrocarbon is 180° C. The primary dilution steam is mixed with the heated heavy hydrocarbon through the pipeline (21) to obtain mixed hydrocarbon. The flow rate of the primary steam is 20 t / h, the temperature is 200° C., and the temperature of the mixed hydrocarbon is 190° C.

[0120] The mixed hydrocarbon is further preheated through the mixed superheating upper section (11), and the temperature of the preheated mixed hydrocarbon is 250°C. The secondary dilution steam is sent to the dilution steam superheater (12) through the pipeline (22) for superheating. The flow rate of the secondary dilution steam is 40t / h. After being superheated to 500°C, it is mixed with the preheated mixed hydrocarbon to obtain the feed of the gas-liquid separation device. The temperature of the feed of the gas-liquid separation device is 320°C. The feed composed of hydrocarbon and steam is in the form of two-phase flow. Gas-liquid separation is performed in the gas-liquid separation device to obtain gas phase material and liquid phase material. The operating temperature of the gas-liquid separation device is 320°C, the operating pressure is 0.33MPaG, and the gasification rate is 75%Wt. The gas phase material is transported to the radiation section furnace tube of the steam cracking furnace for pyrolysis to produce pyrolysis products containing ethylene and deposit coke on the inner wall of the radiation section furnace tube. The operating temperature of the pyrolysis is 820°C, and the operating pressure at the outlet of the radiation section furnace tube is 0.1MPaG. In this embodiment, the pyrolysis product is cooled in a subsequent quenching system, cooled to 420° C. at the beginning of the operation of the cracking furnace, and cooled to 600° C. before the cracking furnace is shut down for coking at the end of the operation.

[0121] Since the cracking furnace will produce coke in the radiation section furnace tube and the quench heat exchanger during the above operation, it is necessary to perform a material withdrawal and coking operation on the cracking furnace. In this embodiment, the hot standby preparation mode before coking is performed, and the material is withdrawn first. The dilution steam process is the same as the cracking furnace operation mode, wherein the amount of primary dilution steam is increased to 25t / h, and the amount of secondary dilution steam is increased to 45t / h. The primary steam and the secondary dilution steam are heated separately in the convection section and mixed to obtain the feed steam of the gas-liquid separation device, and pass through the gas-liquid separation device to remove at least a part of the residue. The temperature of the primary steam after the secondary steam is overheated is 500°C, and the pressure of the primary dilution steam is 0.25MPaG, and the inlet linear velocity is 40m / s. The temperature of the mixed steam is 320°C, the pressure is 0.23MPaG, and the outlet linear velocity is 40m / s. The residual volatile hydrocarbons in some gas-liquid separation devices are purged to the radiation section furnace tubes with the steam.

[0122] The steam containing volatile hydrocarbons is further heated in the radiant section furnace tubes and purged through the furnace tubes. The high temperature steam containing hydrocarbons has a certain dissolving and loosening effect on the coke layer in the furnace tubes. The temperature at the furnace tube outlet is about 800℃. The purging steam is cooled by the quench heat exchanger and then passes through Figure 7 The cracking gas valve TLV and cracking gas pipeline shown are sent to the downstream separation system. After a certain period of purge, open Figure 7 Valve B shown, closed Figure 7 The valve A shown isolates the gas-liquid separator system outside the cracking furnace system, and at the same time closes the cracking gas valve (TLV) and opens the burnt gas valve (DV). At this time, the cracking furnace enters the burnt mode, and as mentioned above, the cracking furnace quench heat exchanger is connected to the burnt tail gas inlet at one end of the burnt tail gas pipeline, and the other end of the burnt tail gas is connected to the cyclone type coke cleaning tank, and then returns to the burner through the return furnace burnt pipeline.

[0123] When the cracking furnace is in a coking mode, a coke tail gas is obtained by passing air or a mixture of steam and air through the radiant section furnace tubes to remove at least a portion of the coke.

[0124] In this embodiment, the temperature of the air after being finally heated in the convection section of the cracking furnace is 550° C., the pressure is 0.22 MPaG, and the inlet linear velocity is 50 m / s. In addition, for the purpose of the coking, the temperature of the steam after being finally heated in the convection section of the cracking furnace is 550° C., the pressure is 0.22 MPaG, and the inlet linear velocity is 50 m / s.

[0125] Bottom and side wall burners are arranged in the furnace of the steam cracking furnace, wherein the number of bottom burners is 48 and the number of side wall burners is 96. Among them, 36 of the bottom burners are used as bottom char burners, and 72 of the side wall burners are used as side wall char burners. The char exhaust gas enters the bottom and side wall char burners of the furnace through the char pipeline for combustion treatment. The operating temperature between the char gas return burners is 380°C and the operating pressure is 0.02MPaG.

[0126] In this embodiment, the char burner includes a central channel and one or more annular channels arranged around the central channel. The central channel is a char exhaust gas channel, the annular channel arranged adjacent to the outer side of the central channel is an air channel, and the annular channel arranged adjacent to the outer side of the air channel is a fuel channel.

[0127] The charred tail gas is transported through the charred tail gas main pipeline, and then transported to the charred burner through a plurality of branch pipelines arranged on the charred tail gas main pipeline. The charred burners are arranged at the bottom and side walls of the furnace. The number of charred burners accounts for 100% of the total number of all burners arranged in the furnace.

[0128] In this embodiment, the charred tail gas delivered to the charred burner arranged at the bottom of the furnace accounts for 75wt% of the total mass of the charred tail gas, and the charred tail gas delivered to the charred burner arranged on the side wall of the furnace accounts for 25wt% of the total mass of the charred tail gas. The total mass flow rate of the charred tail gas is 60t / h. At this time, the inner diameter of the charred tail gas main pipeline is generally 450mm. At least a part of the solid particles are separated from the charred tail gas to obtain purified tail gas, and then the purified tail gas enters the furnace through the at least one charred burner for the combustion treatment. The separation is carried out in a cyclone type coke cleaning tank. At this time, the charred tail gas main pipeline is connected to the outlet of the coke cleaning tank.

[0129] In this embodiment, the solid particle content of the purified tail gas is 30 mg / Nm 3 , based on the total weight of the purified tail gas being 100wt%. The average particle size of the solid particles contained in the purified tail gas is in the range of 1μm-10mm.

[0130] According to this embodiment, the technical effects are detailed in Tables 1 to 3.

[0131] Example 2

[0132] The same as Example 1, except that the heavy hydrocarbon is paraffin-based crude oil, the final distillation point temperature is 800° C., the initial distillation point temperature is 20° C., and the API value of the heavy hydrocarbon is 39.

[0133] According to the embodiment 2, most of the effects of the embodiment 1 can still be achieved, wherein due to the heavier weight of the heavy hydrocarbons, the cracking furnace is likely to produce more coke in the convection section, the radiation section, and the quench heat exchanger, so the operation cycle of the cracking furnace will be shortened, the purge time of the cracking furnace before coking will be longer, and the coking time will also be longer, and the coking effect improvement is slightly reduced compared with the embodiment 1. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0134] Example 3

[0135] The same as Example 1, except that the heavy hydrocarbons are heated to a temperature of 350° C. before being subjected to the gas-liquid separation device.

[0136] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0137] Example 4

[0138] The same as Example 1, except that the operating temperature of the gas-liquid separation device is 370° C., the operating pressure is 0.25 MPaG, and the gasification rate is 80% Wt.

[0139] According to the embodiment 4, most of the effects of the embodiment 1 can still be achieved. Since the operating temperature of the gas-liquid separation device is high, the gasification rate is high, some colloid is entrained in the gas phase material, the coking of the radiation section is accelerated, the operation cycle of the cracking furnace is shortened, and the purging and coking are slightly increased. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0140] Example 5

[0141] The difference from Example 1 is that the operating temperature of the radiation section furnace tube pyrolysis is 820°C, and the operating pressure at the outlet of the radiation section furnace tube is 0.1 MPaG. The technical effects of this example are detailed in Tables 1 to 3.

[0142] Example 6

[0143] The same as Example 1, except that the temperature of the air after being heated in the cracking furnace convection section or by an external heater is 550°C, the pressure is 0.3 MPaG, and the inlet linear velocity is 15 m / s, and the temperature of the steam after being heated in the cracking furnace convection section or by an external heater is 550°C, the pressure is 0.3 MPaG, and the inlet linear velocity is 15 m / s. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0144] Example 7

[0145] The same as Example 1, except that the operating temperature of the charred gas to be burned before returning is 350°C and the operating pressure is 0.05 MPaG. The technical effects of this example are detailed in Tables 1 to 3.

[0146] Example 8

[0147] The same as Example 1, the difference is that the char burner includes a central channel and one or more annular channels arranged around the central channel. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0148] Example 9

[0149] The same as Example 1, the difference is that the burners are evenly arranged at the bottom of the cracking furnace, and each burner is provided with a central channel for receiving the charred tail gas returned to the furnace. The annular channel arranged adjacent to the outer side of the central channel is an air channel, and the annular channel arranged adjacent to the outer side of the air channel is a fuel gas channel. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0150] Example 10

[0151] The same as Example 1, the difference is that the charred tail gas is transported through the charred tail gas main pipeline, and then transported to the charred burner through multiple branch pipelines arranged on the charred tail gas main pipeline, and the number of the multiple branch pipelines is consistent with the number of burners. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0152] Embodiment 11

[0153] The same as Example 1, the difference is that the char burners are arranged at the bottom and side walls of the furnace, and the number of char burners is 80% of the total number of all burners (including bottom and side wall burners). The technical effects of this embodiment are detailed in Tables 1 to 3.

[0154] Example 12

[0155] The same as Example 1, except that the charred tail gas delivered to the charred burner arranged at the bottom of the furnace accounts for 80wt% of the total mass of the charred tail gas, and the charred tail gas delivered to the charred burner arranged on the side wall of the furnace accounts for 20wt% of the total mass of the charred tail gas. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0156] Example 13

[0157] The same as Example 1, the difference is that the mass flow rate of the charred tail gas entering the single unit is 1000 kg / h. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0158] Embodiment 14

[0159] The same as Example 1, except that the charred tail gas is separated from at least a portion of solid particles in the charring tank to obtain purified tail gas, and then the purified tail gas enters the furnace through 36 bottom charring burners and 18 side wall burners for the combustion treatment. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0160] Embodiment 15

[0161] The same as Example 1, the difference is that the separation is carried out in a coke cleaning tank, which is a cyclone type coke cleaning tank. The technical effects of this example are detailed in Tables 1 to 3.

[0162] Example 16

[0163] The same as Example 1, except that the solid particle content of the purified tail gas is 20 mg / Nm3, based on the total weight of the purified tail gas being 100 wt%. The technical effects of this example are detailed in Tables 1 to 3.

[0164] Embodiment 17

[0165] The same as Example 1, except that the average particle size of the solid particles contained in the purified tail gas is 1 μm-15 mm. The technical effects of this example are detailed in Tables 1 to 3.

[0166] Embodiment 18

[0167] The same as Example 1, except that in step A), the temperature of the steam is 480° C., the pressure is 0.3 MPaG, and the inlet linear velocity is 30 m / s.

[0168] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0169] Embodiment 19

[0170] The same as Example 1, except that in step A), the temperature of the mixed steam is 320° C., the pressure is 0.28 MPaG, and the outlet linear velocity is 40 m / s.

[0171] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0172] Embodiment 20

[0173] The same as Example 1, the difference is that before the start of step 3), the gas phase material is stopped from being transported to the radiation section furnace tube.

[0174] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0175] Embodiment 21

[0176] The same as Example 1, except that before step A) starts, the transportation of the heavy hydrocarbons to the gas-liquid separation device is stopped.

[0177] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0178] Embodiment 22

[0179] The same as Example 1, except that after step B) is completed, step 3) is started.

[0180] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0181] Embodiment 23

[0182] The same as Example 1, except that the API value of the heavy hydrocarbon is 35. Since the crude oil is too heavy, the risk of coking of the crude oil in the convection section and the radiation section increases, more coke is generated during operation, the operation cycle becomes shorter, the coking time becomes longer, the amount of coke becomes larger, and the risk of clogging the burner when returning to the furnace to burn coke and the impact on the thermal field in the furnace become larger. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0183] Embodiment 24

[0184] The same as Example 1, except that the temperature of the air after being heated in the cracking furnace convection section or the external heater is 500°C, and the temperature of the steam after being heated in the cracking furnace convection section or the external heater is 500°C. The initial temperature of the air and steam entering the radiant section furnace tube is low, which increases the burner load, and the reaction speed of the air and steam in the furnace tube is reduced in the initial stage, which reduces the decoking effect of the radiant section furnace tube in the front section. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0185] Embodiment 25

[0186] The same as Example 1, the difference is that the char burners are arranged at the bottom and / or side walls of the furnace, and their number is 40% of the total number of all burners arranged in the furnace. The number of burners is small, so the flow rate of char gas in each char burner is high, which easily causes the airflow to jet outward through the center of the burner. Since the char gas carries a large amount of steam and inert gas, it is easy to cause the burner to extinguish. The airflow will also impact the lining and furnace tube of the furnace, causing equipment damage. At the same time, the number of char burners is relatively small, which will also lead to greater unevenness or deviation in the flow distribution of the char gas of each char burner, thereby affecting the uniformity of the thermal field in the entire furnace. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0187] Embodiment 26

[0188] Same as Example 1, except that the solid particle content of the purified tail gas is 40 mg / Nm3, based on the total weight of the purified tail gas being 100 wt%. Since the purified tail gas is not well separated in the cyclone separator, the charred tail gas brought into the charred burner has a high particle content. Since the fuel gas nozzle generally has a small aperture, it is easy to cause blockage of other fuel gas nozzles of the burner. In this embodiment, more than 20% of the burner nozzles are blocked. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0189] Embodiment 27

[0190] Same as Example 1, except that the solid particle content of the purified tail gas is 100 mg / Nm3, based on the total weight of the purified tail gas being 100 wt%. Since the purified tail gas is not well separated in the cyclone separator, the particle content in the charred tail gas brought into the charred burner is relatively high, about 100 mg / Nm3. Since the fuel gas nozzle generally has a small aperture of 2-5 mm, it is very easy to cause the burner fuel gas nozzle to be blocked, thereby causing sintering damage to the burner nozzle, and at the same time causing uneven or insufficient heating in the furnace. In this embodiment, more than 30% of the burner nozzles are sintered and damaged. The technical effects of this embodiment are detailed in Tables 1-3.

[0191] Embodiment 28

[0192] The same as Example 1, the difference is that the burnt tail gas is an annular channel, rather than a channel from the center of the burner upward, which will cause the burnt gas to be too close to the fuel burner, which can easily cause the fuel gas nozzle to extinguish. At the same time, it cannot play a good effect on reducing the flame center temperature and has no good effect on reducing NOx. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0193] Embodiment 29

[0194] The same as Example 1, the difference is that the burnt tail gas of the side wall burnt burner accounts for 70wt% of the total mass of the burnt tail gas. The distribution of the burnt tail gas at the bottom / side wall is unreasonable, resulting in too low a burnt gas amount in the bottom burner and too high a burnt gas amount in the side wall burner. Usually, the heat load of a single side wall burner of a cracking furnace is much smaller than that of the bottom burner, so the processing capacity of the bottom burner is also much larger than that of the side wall burner. The consequence of the uneven distribution is that the side wall burner has the risk of flameout, and at the same time, the particles in the burnt gas cannot obtain a good combustion effect in the side wall burner. The technical effects of this embodiment are detailed in Tables 1-3.

[0195] Embodiment 30

[0196] The same as Example 1, the difference is that in the coking process, the mixed steam is not first obtained through the gas-liquid separator, so it is impossible to bring particles to the coke layer already existing in the furnace tube. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0197] Embodiment 31

[0198] The same as Example 1, the difference is that the temperature of the air after being heated in the convection section of the cracking furnace or by an external heater is 350°C, and the temperature of the steam after being heated in the convection section of the cracking furnace or by an external heater is 350°C. The initial temperature of the air and steam entering the radiant section furnace tube is too low, which greatly increases the burner load, and the reaction speed of the air and steam in the furnace tube in the initial stage is reduced, which greatly reduces the decoking effect of the radiant section furnace tube in the front section. The charring time is increased, which increases the utility consumption. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0199] Embodiment 32

[0200] The same as Example 1, except that the steam inlet linear velocity is 90 m / s. Since the linear velocity of the steam before entering the radiation section furnace tube is too high, the pipeline before entering the furnace tube vibrates, and the system pressure drop is too large, which increases consumption. Under long-term vibration, the pipeline is prone to stress tearing, resulting in equipment damage. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0201] Embodiment 33

[0202] The same as Example 1, except that the linear velocity of the steam inlet is 15 m / s. Since the linear velocity of the steam before entering the radiation section furnace tube is too low, the Venturi does not throttle, resulting in uneven distribution of fluid in the furnace tube, causing local furnace tube overheating. As a result, the cracking furnace needs to reduce the load and lower the operating temperature, which prolongs the coking operation time. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0203] Embodiment 34

[0204] The same as Example 1, the difference is that only all 48 bottom burners are used as char burners. The technical effects of this example are detailed in Tables 1 to 3.

[0205] Embodiment 35

[0206] The same as Example 1, the difference is that only all 96 side wall burners are used as char burners. The technical effects of this example are detailed in Tables 1 to 3.

[0207] Embodiment 36

[0208] The same as Example 1, except that the heavy hydrocarbons are heated to a temperature of 150°C before the gas-liquid separation. The technical effects of this example are detailed in Tables 1 to 3.

[0209] Comparative Example 1

[0210] The same as Example 1, except that ethane is used as the steam cracking raw material. The technical effects of this example are detailed in Tables 1 to 3.

[0211] Comparative Example 2

[0212] The same as Example 1, except that naphtha is used as steam cracking raw material. The technical effects of this example are detailed in Tables 1 to 3.

[0213] Comparative Example 3

[0214] The same as Example 1, the difference is that the conventional method is used to return to the furnace, that is, only the charred opening between the burners is returned to the furnace. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0215] As shown in Tables 1 to 3, by comparing the data of Examples 1-35 (especially Example 1-22) with those of Comparative Examples 1-3, it can be seen that the charring method using heavy hydrocarbons mentioned in the present invention can reduce the charring time by an average of about 20%, reduce the concentration of flue gas particulate matter by about 30%, reduce NOx emissions in the flue gas by about 30%, reduce the COT deviation during charring by more than 10°C, and save more than 5 million yuan in economic losses.

[0216]

[0217]

[0218]

Claims

1. A coking method for a steam cracking furnace, comprising the following steps: 1) subjecting heavy hydrocarbons to gas-liquid separation in a gas-liquid separation device to obtain gas phase material and liquid phase material, and depositing residue on the inner wall of the gas-liquid separation device, 2) transporting the gaseous material to a radiant section furnace tube of a steam cracking furnace for pyrolysis to produce a pyrolysis product containing ethylene and depositing coke on the inner wall of the radiant section furnace tube; 3) passing air and / or steam through the radiant section furnace tubes to remove at least a portion of the coke to obtain a charred tail gas, 4) The charred tail gas is allowed to enter the furnace of the steam cracking furnace through at least one burner (called a charred burner) disposed in the furnace for combustion treatment.

2. The method according to claim 1, wherein in step 1), the final distillation point temperature of the heavy hydrocarbon is above 540°C (preferably the initial distillation point temperature is 15°C and the final distillation point temperature is above 750°C), and / or the API value of the heavy hydrocarbon is not less than 32 (preferably above 38), and / or the heavy hydrocarbon is selected from at least one of paraffin-based crude oil, intermediate-based crude oil, cycloalkyl crude oil, condensate oil and refined products.

3. The method according to claim 1, wherein in step 1), the heavy hydrocarbons are heated to a temperature of 100-400°C (preferably 200-370°C) before the gas-liquid separation.

4. The method according to claim 1, wherein in step 1), the operating temperature of the gas-liquid separation is 260-360°C, the operating pressure is 0.2-0.7 MPaG, and the gasification rate is 50-80wt%.

5. The method according to claim 1, wherein in step 2), the operating temperature of the pyrolysis is 800-900°C and the operating pressure is 0.05-0.15 MPaG.

6. The method of claim 1, wherein the pyrolysis product is cooled to 400-600°C by passing through a quench heat exchanger.

7. The method according to claim 1, wherein in step 3), the temperature of the air is 500-650°C, the pressure is 0.2-0.4 MPaG, and the inlet linear velocity is 30-80 m / s, and the temperature of the steam is 500-650°C, the pressure is 0.2-0.4 MPaG, and the inlet linear velocity is 30-80 m / s.

8. The method according to claim 1, wherein in step 4), the operating temperature of the combustion treatment is 300-400°C and the operating pressure is 0.05-0.1 MPaG.

9. The method of claim 1, wherein in step 4), the char burner comprises a central channel and one or more annular channels arranged around the central channel.

10. The method of claim 9, wherein the central channel is a burnt exhaust gas channel, the annular channel disposed adjacent to the outer side of the central channel is an air channel, and the annular channel disposed adjacent to the outer side of the air channel is a fuel channel.

11. The method according to claim 1, wherein in step 4), the charred tail gas is transported through a charred tail gas main pipeline, and then transported to the charred burner through a plurality of branch pipelines arranged on the charred tail gas main pipeline.

12. The method of claim 1, wherein in step 4), the charring burners are arranged at the bottom and / or side walls of the furnace, and their number is 20-100% (preferably 50-100% or 100%) of the total number of all burners provided in the furnace.

13. The method according to claim 12, wherein the charred tail gas delivered to the charred burner arranged at the bottom of the furnace accounts for 50-100wt% (preferably 65-85wt%) of the total mass of the charred tail gas, and the charred tail gas delivered to the charred burner arranged on the side wall of the furnace accounts for 0-50wt% (preferably 15-35wt%) of the total mass of the charred tail gas.

14. The method according to claim 1, wherein in step 4), the total mass flow rate of the charred tail gas is 40-120 t / h.

15. The method according to claim 1, wherein in step 4), at least a portion of solid particles are separated from the charred tail gas to obtain purified tail gas, and then the purified tail gas enters the furnace through the at least one charred burner for the combustion treatment.

16. The method of claim 15, wherein the separation is carried out in a decoking drum (preferably a cyclone decoking drum).

17. The method of claim 15, wherein the solid particle content of the purified tail gas is less than 50 mg / Nm 3 (Preferably less than 20 mg / Nm 3 ), based on the total weight of the purified tail gas being 100wt%.

18. The method of claim 15, wherein the particle size of the solid particles contained in the purified tail gas is in the range of 1 μm-20 mm (preferably 1 μm-10 mm).

19. The method of claim 1, further comprising the steps of: A) passing steam through the gas-liquid separation device to remove at least a portion of the residue to obtain mixed steam, B) transporting the mixed steam through the radiant section furnace tubes to remove at least a portion of the coke to obtain the charring tail gas.

20. The method of claim 19, wherein in step A), the steam has a temperature of 400-500°C, a pressure of 0.2-0.7 MPaG, and an inlet linear velocity of 20-50 m / s.

21. The method of claim 19, wherein in step A), the temperature of the mixed steam is 250-400°C, the pressure is 0.2-0.4 MPaG, and the outlet linear velocity is 25-40 m / s.

22. The method of claim 1, wherein before step 3) begins, the gas-phase material is stopped from being transported to the radiant section furnace tube.

23. The method of claim 19, wherein before step A) starts, the conveying of the heavy hydrocarbons to the gas-liquid separation device is stopped.

24. The method of claim 19, wherein after step B) is completed, step 3) is started.

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