Coke burning method of steam cracking furnace

Abstract

The present invention relates to a coke burning method of a steam cracking furnace. The coke burning method of a steam cracking furnace of the present invention comprises the following steps: 1) subjecting heavy hydrocarbons to gas-liquid separation 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 into a radiant section furnace tube of a steam cracking furnace to perform pyrolysis so as to generate a pyrolysis product containing ethylene and deposit 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 part of the coke, so as to obtain coke-burning tail gas; and 4) making the coke-burning tail gas enter a hearth via at least one burner disposed in the hearth of the steam cracking furnace and undergo a combustion treatment. The present invention can effectively solve the decoking problem of a gas-liquid separation device of a heavy-hydrocarbon cracking furnace.

Description

A coking method for a steam cracking furnace Technical Field

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

[0002] With economic development, the demand for hydrocarbon chemical raw materials is increasing. As an important chemical raw material, ethylene's application market is also expanding. Hydrocarbon cracking to produce ethylene is currently the mainstream process for producing ethylene in the market.

[0003] During the operation of the cracking furnace, when hydrocarbons are thermally cracked at high temperatures, catalytic coking, free radical coking, and condensation coking will occur on the inner surface of the radiant section tubes of the cracking furnace. 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 radiant section tubes and the quench heat exchanger. The coke will increase the heat transfer resistance, causing the wall temperature of the radiant section tubes to rise and the temperature of the cracked gas at the outlet of the quench heat exchanger to rise. Therefore, to avoid overheating, the coke produced by the radiant section tubes and other parts needs to be regularly burned. The burnt tail gas produced by the burnt tail gas includes carbon oxides, water vapor, and residual coke particles. The temperature of the burnt tail gas from the cracking furnace is relatively high, generally in the range of 200-500℃.

[0004] For cracking furnaces containing high-boiling-point heavy hydrocarbon feedstocks, the currently available method is to preheat the feedstock, then separate the undesirable materials through a gas-liquid separator, and then feed the suitable materials to the cracking furnace for cracking. This process also easily produces residual oil and coke in the gas-liquid separation system, resulting in significant pressure drop resistance and affecting the normal operation of the cracking furnace.

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

[0006] For a heavy hydrocarbon feedstock cracking furnace, CN102227488B discloses a method for decoking a gas-liquid separation device. This method passes a mixture of steam and air into the gas-liquid separation device for incineration, and the coke residue after incineration passes through a decoking circulation pipe between the cracking furnace burners and returns to the furnace.

[0007] Summary of the Invention

[0008] 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 to burn.

[0009] According to a first aspect of the present invention, a coking method for 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 gaseous and liquid materials, and depositing residue on the inner wall of the gas-liquid separation device; 2) conveying the gaseous materials to the radiant section furnace tubes of the steam cracking furnace for pyrolysis to produce pyrolysis products containing ethylene and depositing coke on the inner wall of the radiant section furnace tubes; 3) conveying air and / or steam through the radiant section furnace tubes to remove at least a portion of the coke to obtain coked tail gas; and 4) allowing the coked tail gas to enter the furnace of the steam cracking furnace through at least one burner arranged in the furnace for combustion treatment.

[0010] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG1 shows an overall schematic diagram of a method 2 mentioned in the background of the present invention in which a separate charring port is provided at the bottom of the return furnace.

[0012] FIG2 shows a detailed schematic diagram of a separate charring port provided at the bottom of the return furnace in solution 2 mentioned in the background of the present invention.

[0013] FIG3 shows a schematic diagram of the subsequent connection structure of the burnt tail gas pipeline of the comprehensive treatment system for burnt tail gas from a heavy hydrocarbon cracking furnace according to the present invention.

[0014] FIG4 shows a schematic diagram of the subsequent connection structure of the burnt tail gas pipeline of the comprehensive treatment system for burnt tail gas from a heavy hydrocarbon cracking furnace according to the present invention.

[0015] FIG5 shows 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 according to the present invention.

[0016] FIG6 shows 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.

[0017] FIG7 shows a schematic diagram of a comprehensive treatment system for charred tail gas from a heavy hydrocarbon cracking furnace provided by the present invention.

[0018] The accompanying drawings are marked as follows: 1-burned tail gas pipeline, 2-coke cleaning tank, 3-main pipeline, 4.1-bottom burner, 4.2-side wall burner, 5-furnace of the cracking furnace radiation section, 6-branch line, 7-return furnace burner port; 8-quenching 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; 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-burned tail gas, 24-cracking gas.

[0019] Technical Effects

[0020] 1. The inventors of the present invention have discovered that the coke produced in the furnace tubes during the operation of a 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 large 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 the existing cracking furnace coke gas returning to the furnace with a separate airflow impact, 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 tubes.

[0021] 2. The present invention addresses the characteristics of the heavy hydrocarbon cracking furnace process, which contains a unique gas-liquid separation device. Before coking, 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 radiant section furnace tubes. The volatile hydrocarbons contained in the mixed steam help loosen and remove the coke on the furnace tubes, thereby improving the coke cleaning effect in the furnace tubes during coking.

[0022] 3. The system of the present invention effectively solves the decoking problem in the gas-liquid separation unit of a heavy hydrocarbon cracking furnace, avoiding the safety risk of direct contact between charred air and hydrocarbons, and preventing equipment damage. Furthermore, system switching is simple, eliminating the need to empty the gas-liquid separation system, reducing operational workload and avoiding safety hazards caused by misoperation.

[0023] 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.

[0024] 5. The same number of return pipes as burners is provided, and these branch pipes are connected to dedicated nozzles for burnt exhaust gas within the burners. Compared to the prior art (Scheme 2) that provides a separate burner port at the bottom of the furnace, the branch pipes for the return pipes provided in this invention are smaller and occupy less space, resolving the issue of difficult placement of return pipes and burner ports. Furthermore, because the burner ports are located away from the furnace tubes, scouring of the tubes and damage to the tubes caused by water carried by the return steam are avoided.

[0025] 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 intermingling, causing pipeline overheating, combustion disorder, etc.

[0026] 7. It has a better combustion effect on the particles in the charred gas, which can reduce the requirements for the charred tank. Currently, the charred tank must reach a particle size of 20mg / Nm 3 The emission requirements are more difficult to meet. The main function of the coke pot 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 do not come into direct contact with the burning flame, the combustion effect is poor, which will cause the particles at the cracking furnace chimney outlet to exceed the standard (ultimately exceeding 20mg / Nm 3 The burner can improve the effect of particle burning, which can reduce the requirements of the burning tank on the one hand, and prevent the unburned particles from being carried to the convection section to cause dust accumulation on the fins or remaining at the bottom of the furnace and affecting the flue gas circulation on the other hand.

[0027] 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. Based on the characteristics of the coke produced by direct cracking of crude oil and the characteristics of the coke particles returning to the furnace, the present invention proposes a new idea to improve the coking effect. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are described in detail below. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the claims in the appendix.

[0029] 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 commonly understood by those skilled in the art. In the event of conflict, the definitions in this specification will prevail.

[0030] 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, the objects introduced by the prefix include 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 generally recognized in the art to be suitable for similar purposes.

[0031] 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.

[0032] In the context of the present invention, “substantially” means that deviations that are acceptable or reasonable to those skilled in the art are allowed, such as deviations within ±2%, within ±1%, within ±0.5% or within ±0.1%.

[0033] In the context of the present invention, the terms "primary dilution steam", "secondary dilution steam" and the like are only used to distinguish the steam introduced in different steps, and do not contain any actual meaning such as the properties of the steam itself.

[0034] In the context of the present invention, unless otherwise specified, the various devices used in the present invention may use structures conventionally selected in the art without particular limitation.

[0035] In the context of the present invention, heavy hydrocarbons refer to mixed hydrocarbons with a broad distillation range, typically with a final boiling point above 540°C, for example, an initial boiling point of 15°C and a final boiling point of approximately 750°C. Specifically, these heavy hydrocarbons can be selected from one or more of the following feedstocks: paraffinic crude oil, intermediate crude oil, naphthenic crude oil, condensate oil, and refined products. Examples of refined products include gasoline, kerosene, diesel, tail oil, fuel oil, and reformate oil, which are processed in refineries through atmospheric and vacuum distillation, reforming, catalytic, and coking units.

[0036] In the context of the present invention, the initial boiling point, final boiling point and distillation range are measured by 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.

[0037] In the context of the present invention, API refers to specific gravity index, and its analysis method adopts ASTM D-2320.

[0038] In the context of the present invention, the method for measuring the solid particle content is the light scattering method.

[0039] In the context of the present invention, the method of measuring the average particle size is laser light scattering.

[0040] In the context of the present invention, the gasification rate refers to the mass percentage of gas phase material (excluding steam) to the total amount of feed (excluding steam).

[0041] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight and pressure is gauge pressure.

[0042] 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 scope of protection of the present invention.

[0043] According to one embodiment of the present invention, a coking method for a steam cracking furnace is provided.

[0044] 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 radiant section furnace tubes of the cracking furnace, and secondary reaction coking and condensation coking will occur on the inner surface of the quench heat exchanger. The generated coke adheres to the inner wall of the radiant section furnace tubes and the quench heat exchanger. The generated coke will increase the heat transfer resistance, causing the wall temperature of the radiant section furnace tubes to rise and the temperature of the cracked gas at the outlet of the quench heat exchanger to rise. Therefore, in order to avoid overheating, the coke generated by the radiant section furnace tubes, etc. needs to be regularly burned.

[0045] According to one embodiment of the present invention, the coking method includes the 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 helps the subsequent coking and removal of coke from the furnace tube.

[0046] According to one embodiment of the present invention, the final boiling point temperature of the heavy hydrocarbon is above 540°C (preferably, the initial boiling point temperature is 15°C and the final boiling point 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.

[0047] 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 carried out in the convection section of the cracking furnace.

[0048] 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. Furthermore, the present invention also does not particularly limit the operating conditions of the gas-liquid separation. However, by way of example, the operating temperature of the gas-liquid separation is generally 260-360°C, the operating pressure is generally 0.2-0.7 MPaG, and the gasification rate is generally 50-80%.

[0049] According to one embodiment of the present invention, the coking method includes 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 inventors of the present invention have found that filamentous coke is formed on the furnace tube due to catalytic coking, while tar droplets or coke particles are formed by free radical coking or gas phase coking and uniformly adhere to the surface of the furnace tube, eventually forming a stable coking layer, and the coking layer becomes thicker with increasing operating time. Coking increases the heat transfer resistance of the cracking furnace tube wall, reduces the heat transfer coefficient, causes the outer wall temperature of the furnace tube to increase, and causes local overheating, which shortens the service life of the furnace tube.

[0050] According to the present invention, there are no limitations on the specific structures of the cracking furnace and the radiant section furnace tubes, nor on the operating conditions of the pyrolysis process. Conventional steam cracking techniques can be directly applied. For example, the pyrolysis process typically operates at a temperature of 800-900°C and a pressure of 0.06-0.15 MPaG.

[0051] According to one embodiment of the present invention, the coking method includes step 3): passing air and / or steam through the radiant furnace tubes to remove at least a portion of the coke (referred to as coking scheme 1), thereby producing coking tail gas. The air and steam may be used separately or in combination. When used in combination, the ratio of air to steam may be selected within a range commonly known in the art and is not particularly limited.

[0052] According to one embodiment of the present invention, the pyrolysis products are cooled, preferably to a temperature of 400-600°C, via a quench heat exchanger. According to the present invention, since the pyrolysis products are transported through the quench heat exchanger, coke deposition also occurs in the quench heat exchanger. To this end, the coking method of the present invention also includes a process of coking the quench heat exchanger. For example, in step 3), air and / or steam can be sequentially transported through the radiant furnace tubes and the quench heat exchanger to remove at least a portion of the coke (referred to as coking scheme 2), thereby obtaining the coked tail gas.

[0053] According to one embodiment of the present invention, in step 3), for the purpose of charring, the air temperature is 500-650°C, the pressure is 0.2-0.4 MPaG, and the inlet linear velocity is 30-80 m / s. Furthermore, for the purpose of charring, the steam temperature is 500-650°C, the pressure is 0.2-0.4 MPaG, and the inlet linear velocity is 30-80 m / s. According to the present invention, the air and steam can be brought to these operating conditions by any conventional means known in the art, such as heating to the desired temperature, particularly through the convection section of the cracking furnace or a separately provided preheater, without particular limitation. Furthermore, the so-called inlet linear velocity refers to the linear velocity of the air or steam at the inlet of the radiant section furnace tubes. The inventors of the present invention have discovered that if the air or steam temperature is too low, the starting temperature of the charring reaction will not be reached, the charring effect will not be achieved, the charring time will be prolonged, and more fuel will be consumed. If the air or steam temperature is too high, local hot spots can easily result, causing overheating and damage to the furnace tubes. The inventors of the present invention also discovered that if the air or steam inlet linear velocity is too low, the air or steam will be unevenly distributed in different groups of furnace tubes, resulting in temperature deviations between the furnace tubes and causing some furnace tubes to overheat. If the air or steam inlet linear velocity is too high, the pressure drop in the furnace tubes will be too large, significantly increasing the overall operating costs of the system and also causing furnace tube flow deviation.

[0054] According to one embodiment of the present invention, before step 3) begins, the gaseous material is stopped from being transported to the radiant furnace tubes, i.e., the operation of step 2) is stopped. Therefore, according to this embodiment of the present invention, pyrolysis and charring are two independent steps and are not performed simultaneously.

[0055] 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, thereby obtaining mixed steam. The inventors of the present invention have discovered that if air is conveyed into the gas-liquid separation device, the air and residual hydrocarbons within the gas-liquid separation device may explode, posing a safety hazard. The inventors of the present invention have also discovered that by conveying steam into the gas-liquid separation device, the purge effect of the steam can be utilized to vaporize at least a portion of the residue (primarily volatile hydrocarbons) and be entrained in the steam, thereby forming a mixture of the steam and the volatile hydrocarbons, i.e., the mixed steam.

[0056] 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 purge effect becomes worse, the purge 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 purge 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, which increases the operating costs. At the same time, too fast a flow rate will cause pipeline vibration, which is easy to cause safety hazards.

[0057] 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 found that if the temperature of the mixed steam is too low, the temperature of the mixed steam entering the radiation section is low, affecting the charring effect of the furnace tube, and if the temperature of the mixed steam is too high, it is easy to cause pipelines or equipment to overheat. The inventors of the present invention also found that if the outlet linear velocity of the mixed steam is too low, it affects the uniformity of the distribution of the mixed steam 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.

[0058] According to one embodiment of the present invention, the coking method further includes step B): transporting the mixed steam through the radiant section furnace tube to remove at least a portion of the coke (referred to as coking scheme three) to obtain coking tail gas. As mentioned above, the inventors of the present invention 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 purge to the radiant 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 helps the subsequent furnace tube coking and coke removal.

[0059] According to one embodiment of the present invention, before step A) begins, the delivery of the heavy hydrocarbons to the gas-liquid separation device is stopped, 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 independent steps and are not performed simultaneously.

[0060] According to one embodiment of the present invention, after step B) is completed, step 3) is started, that is, the mixed steam is first conveyed through the radiation section furnace tube to remove at least a portion of the coke (called 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 found that in order to effectively prevent air from entering the gas-liquid separation device, step B) and step 3) cannot be performed at the same time, but must be performed one after another. 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 and will cause explosion, posing a safety hazard.

[0061] According to one embodiment of the present invention, the charring method includes step 4): passing the charred tail gas into the furnace of the steam cracking furnace via at least one burner (referred to as a charring burner) disposed therein for combustion. In the context of the present invention, any tail gas obtained from charring is collectively referred to as charred tail gas, regardless of the specific charring method.

[0062] According to one embodiment of the present invention, there is no particular limitation on the operating conditions of the combustion treatment, and conventionally known contents in the art can be directly applied. However, 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.

[0063] 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 the char exhaust gas channel, the annular channel arranged adjacent to the outside of the central channel is the air channel, and the annular channel arranged adjacent to the outside of the air channel is the fuel channel. The inventors of the present invention have found that a burner with this specific structure is particularly suitable for use as the char burner of the present invention.

[0064] According to one embodiment of the present invention, in step 4), the charred tail gas is transported through a main charred tail gas pipeline and then delivered to the charred burner via multiple branch lines provided on the main charred tail gas pipeline. Generally, the number of branch lines is equal to the number of charred burners, thereby ensuring that one branch line corresponds to one charred burner. Depending on the specific charring scheme, the main charred tail gas pipeline can be connected to the outlet of the radiant section furnace tubes or the outlet of the quench heat exchanger, without any particular limitation.

[0065] According to one embodiment of the present invention, in step 4), the char burners are arranged at the bottom and / or side walls of the furnace, preferably at both the bottom and side walls. Furthermore, according to the present invention, there is no particular limitation on the number of char burners, but they generally represent 20-100% of the total number of burners in the furnace, preferably 50-100% or 100%.

[0066] According to one embodiment of the present invention, the charred tail gas delivered to the charred burner disposed at the bottom of the furnace accounts for 50-100 wt% (preferably 65-85 wt%) of the total mass of the charred tail gas, and the charred tail gas delivered to the charred burner disposed on the side wall of the furnace accounts for 0-50 wt% (preferably 15-35 wt%) of the total mass of the charred tail gas. The inventors of the present invention have found that the load of the side wall burners generally accounts for 10%-30% of the total combustion load, and therefore the amount of charred tail gas entering the side wall burners is commensurate with this load.

[0067] 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. In this case, the inner diameter of the charred tail gas main pipeline is generally 250-800 mm.

[0068] 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, which is then passed through the at least one charred burner into the furnace for combustion. According to the present invention, the separation can be performed using any conventional gas-solid separation method known in the art, without particular limitation. For example, the separation is performed in a coke cleaning tank (preferably a cyclone-type coke cleaning tank). In this case, the charred tail gas main line can be connected to the outlet of the coke cleaning tank.

[0069] 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 20 mg / Nm 3, based on the total weight of the purified tail gas as 100wt%. Preferably, the average particle size of the solid particles contained in the purified tail gas is in the range of 1μm-20mm (preferably less than 10mm). The inventors of the present invention have found that the present invention has a better combustion effect on the particles in the char gas and can reduce the requirements for the char tank. At present, the char tank needs to achieve a particle size of 20mg / Nm 3 The emission requirements are more difficult to meet. The main function of the coke pot 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 do not come into direct contact with the burning flame, the combustion effect is poor, which will cause the particles at the cracking furnace chimney outlet to exceed the standard (ultimately exceeding 20mg / Nm 3 The burner can improve the effect of particle burning, which can reduce the requirements of the burning tank on the one hand, and prevent the unburned particles from being carried to the convection section and causing dust accumulation on the fins or remaining at the bottom of the furnace, affecting the flue gas circulation.

[0070] The present invention will be 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.

[0071] 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 quenching heat exchanger, a burnt tail gas pipeline, a return furnace pipeline, and optionally a coke cleaning tank.

[0072] According to one embodiment of the present invention, the convection section of the cracking furnace includes 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.

[0073] 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 quenching heat exchanger in sequence.

[0074] According to one embodiment of the present invention, the other end of the burnt tail gas pipeline, the return furnace pipeline and the burner that introduces the burnt tail gas are connected in sequence, or the other end of the burnt tail gas pipeline, the coke cleaning tank, the return furnace pipeline and the burner that introduces the burnt tail gas are connected in sequence.

[0075] 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.

[0076] According to one embodiment of the present invention, preferably, the dilution steam superheating section includes 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.

[0077] 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.

[0078] 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.

[0079] According to one embodiment of the present invention, the liquid phase outlet of the gas-liquid separation device is connected to the outside.

[0080] 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.

[0081] According to one embodiment of the present invention, each burner into which the charred tail gas is introduced is correspondingly connected to a branch line, and is connected to the main line through the branch line.

[0082] According to one embodiment of the present invention, the coke cleaning tank is a cyclone type coke cleaning tank.

[0083] 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 connected only to the branch line.

[0084] 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%.

[0085] According to one embodiment of the present invention, the burner for introducing the burnt tail gas is arranged at the bottom and / or side wall of the furnace of the radiation section of the cracking furnace.

[0086] According to the comprehensive treatment method of the heavy hydrocarbon cracking furnace charred tail gas of the present invention, the method adopts the above-mentioned system and comprises the following steps:

[0087] 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 residual hydrocarbons in the gas-liquid separation device to obtain 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

[0088] Feeding steam and optionally air into the cracking furnace convection section to heat the obtained heated gas and feeding it into the inlet of the lower superheating section through the second valve;

[0089] S2: subjecting the mixture or heated gas to heating in the lower superheating section and charring in the radiant section of the cracking furnace in sequence to obtain charred tail gas;

[0090] S3: sending the burnt tail gas into 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,

[0091] The burnt tail gas is sent to the decoking tank for treatment through the quench heat exchanger and the burnt tail 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.

[0092] 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.

[0093] According to one embodiment of the present invention, the final distillation point of the heavy hydrocarbon is above 540°C.

[0094] According to one embodiment of the present invention, the steam includes steam fed into the primary dilution steam superheating section and / or steam fed into the secondary dilution steam superheating section.

[0095] According to one embodiment of the present invention, the charring tail gas includes at least one of steam, carbon oxides, air and coke powder.

[0096] 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.

[0097] According to one embodiment of the present invention, the mass flow rate of the charred tail gas fed into the burner disposed 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 charred tail gas, preferably 65%-85%; the mass flow rate of the charred tail gas fed into the burner disposed 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 charred 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.

[0098] The present invention will be further described below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0099] The comprehensive treatment system for burnt tail gas from a cracking furnace according to the present invention is shown in FIG3 . The system includes a burnt tail gas pipeline 1, a return furnace pipeline, a burner, a cracking furnace radiation section furnace 5, and a coke cleaning tank 2; the cracking 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 for the burnt tail gas; the other end of the burnt tail gas pipeline 1, the coke cleaning 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, each of which 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, as shown in FIG6 , one of which is connected only to the branch pipeline 6. The coke cleaning tank 2 is a cyclone-type coke cleaning tank.

[0100] 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 coke cleaning tank 2 through the charred tail gas pipeline 1 for preliminary separation treatment, and then sent from the coke cleaning tank 2 through the return furnace pipeline into the burners arranged at the bottom and side walls of the cracking furnace radiation section furnace 5 for combustion treatment.

[0101] According to another comprehensive treatment system for burnt tail gas from a cracking furnace of the present invention, as shown in Figures 4 and 5, 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 for the burnt tail gas; the other end of the burnt tail gas pipeline 1, the return furnace pipeline, and the burner for introducing the burnt tail gas are connected in sequence; there are multiple burners for introducing the burnt tail gas. The return furnace pipeline includes multiple main pipelines 3, 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 for introducing the burnt tail gas is provided with multiple nozzles, as shown in Figure 6, one of which is only connected to the branch pipeline 6.

[0102] According to the present invention, the comprehensive treatment method of the cracking furnace burnt tail gas using the above-mentioned system includes the following steps: the burnt tail gas generated by the cracking furnace burnt treatment is sent into 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.

[0103] Example

[0104] The present invention is further described in detail below using examples and comparative examples, but the present invention is not limited to these examples.

[0105] The raw materials used in the examples and comparative examples were all obtained from commercial sources.

[0106] The comparison indicators in the embodiments and comparative examples are the duration of charring, the concentration of particulate matter emissions in the flue gas, the NOx emission index in the flue gas, the deviation of the furnace tube outlet temperature (COT) during charring, the online operation time of the cracking furnace throughout the year, the equipment maintenance fee, the economic loss fee, etc.

[0107] The coking time refers to the total time from the start of coking to the end of coking when the cracking furnace performs a single coking operation.

[0108] The method for measuring the NOx emission index in the flue gas is a chemiluminescence online monitoring method.

[0109] The COT deviation of the furnace tube 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.

[0110] The annual online operation time of the cracking furnace refers to the total time of the cracking furnace during the feeding operation period.

[0111] The equipment maintenance fee is based on the one-time equipment renewal purchase fee.

[0112] The economic loss fee is calculated based on the average market price of high value-added products in the past three years.

[0113] Example 1

[0114] Heavy hydrocarbons are used as feed to the cracking furnace for steam cracking. The heavy hydrocarbons are a wide-fraction crude oil, and low-sulfur paraffin-based crude oil with an API value of 44 is used. The initial boiling point of the heavy hydrocarbons is 15°C and the final boiling point is 800°C.

[0115] As shown in FIG7 , the system includes a cracking furnace, a gas-liquid separation device (14), a coke removal tank (2), and a quench heat exchanger (8). The cracking furnace includes a heavy hydrocarbon preheating section (10), an upper mixed superheating section (11), a dilution steam superheating section (12), a lower mixed superheating section (13), a radiant section furnace tube (15), a primary dilution steam feed line (21), a secondary dilution steam feed line (22), and an air feed line (17).

[0116] In the cracking furnace operation mode, the heavy hydrocarbons first enter the heavy hydrocarbon preheating section (10) at the upper portion of the cracking furnace for preheating. The feed rate of the heavy hydrocarbons is 100 t / h. The temperature of the preheated heavy hydrocarbons is 180°C. Primary dilution steam is mixed with the heated heavy hydrocarbons through a pipeline (21) to obtain mixed hydrocarbons. The primary steam has a flow rate of 20 t / h and a temperature of 200°C. The temperature of the mixed hydrocarbons is 190°C.

[0117] The mixed hydrocarbons are further preheated by the upper mixed superheating section (11). The temperature of the preheated mixed hydrocarbons is 250°C. Secondary dilution steam is sent to the dilution steam superheater (12) through the pipeline (22) for superheating. The secondary dilution steam has a flow rate of 40 t / h. After being superheated to 500°C, it is mixed with the preheated mixed hydrocarbons to obtain the feed for the gas-liquid separation device. The feed temperature of the gas-liquid separation device is 320°C. The feed consisting of hydrocarbons and steam is in the form of a two-phase flow. Gas-liquid separation is carried out 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 0.33 MPaG, and the gasification rate is 75% Wt. The gas phase material is transported to the radiant 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 radiant section furnace tube. The operating temperature of the pyrolysis is 820°C, and the operating pressure at the outlet of the radiant section furnace tube is 0.1 MPaG. In this embodiment, the pyrolysis products are cooled in a subsequent quenching system, cooled to 420° C. at the beginning of the cracking furnace operation, and cooled to 600° C. before the cracking furnace is shut down for coking at the end of the operation.

[0118] Because the cracking furnace produces coke in the radiant tubes and quench heat exchanger during the aforementioned operation, it is necessary to perform a feed removal and coking operation on the cracking furnace. In this embodiment, a hot standby mode is used before coking, first removing the feed. The dilution steam process is the same as the cracking furnace operation mode, with the primary dilution steam rate increased to 25 t / h and the secondary dilution steam rate increased to 45 t / h. The primary and secondary dilution steam are heated separately in the convection section and mixed to form feed steam for the gas-liquid separator, which then passes through the gas-liquid separator to remove at least a portion of the residue. The primary steam, after secondary steam superheating, has a temperature of 500°C, a pressure of 0.25 MPaG, and an inlet linear velocity of 40 m / s with the primary dilution steam. The mixed steam has a temperature of 320°C, a pressure of 0.23 MPaG, and an outlet linear velocity of 40 m / s. Some of the residual volatile hydrocarbons in the gas-liquid separator are purged with the steam into the radiant tubes.

[0119] The steam containing volatile hydrocarbons is further heated in the radiant section furnace tubes and purged. The high-temperature hydrocarbon-containing steam has a certain dissolving and loosening effect on the coke layer within the furnace tubes, with the temperature at the furnace tube outlet reaching approximately 800°C. The purge steam is cooled in a quench heat exchanger and then delivered to the downstream separation system via the cracked gas valve TLV and cracked gas pipeline shown in Figure 7. After a certain period of purging, valve B (Figure 7) is opened and valve A (Figure 7) is closed, isolating the gas-liquid separator system from the cracking furnace system. Simultaneously, the cracked gas valve (TLV) is closed and the burnt gas valve (DV) is opened. The cracking furnace now enters the burn mode. As previously described, the cracking furnace quench heat exchanger is connected to the burnt tail gas inlet at one end of the burnt tail gas pipeline. The other end of the burnt tail gas is connected to a cyclonic coke cleaning tank, and then returned to the burner via the return burner pipeline.

[0120] 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 tubes to remove at least a portion of the coke.

[0121] In this embodiment, the air is finally heated in the convection section of the cracking furnace at a temperature of 550°C, a pressure of 0.22 MPaG, and an inlet linear velocity of 50 m / s. Furthermore, for the purpose of coking, the steam is finally heated in the convection section of the cracking furnace at a temperature of 550°C, a pressure of 0.22 MPaG, and an inlet linear velocity of 50 m / s.

[0122] The steam cracking furnace is equipped with bottom and sidewall burners, totaling 48 bottom burners and 96 sidewall burners. Thirty-six of the bottom burners are used as bottom char burners, and 72 of the sidewall burners are used as sidewall char burners. The char exhaust gas is fed through a char pipeline into the bottom and sidewall char burners of the furnace for combustion. The operating temperature between the char exhaust burners is 380°C, and the operating pressure is 0.02 MPaG.

[0123] In this embodiment, the scorch burner includes a central channel and one or more annular channels arranged around the central channel. The central channel is a scorch exhaust gas channel, the annular channels arranged immediately outside the central channel are air channels, and the annular channels arranged immediately outside the air channels are fuel channels.

[0124] The charred tail gas is transported through a main charred tail gas pipeline and then transported to the charred tail gas burners through multiple branch pipelines installed on the main charred tail gas pipeline. The charred tail gas burners are arranged at the bottom and side walls of the furnace. The number of charred tail gas burners accounts for 100% of the total number of burners installed in the furnace.

[0125] 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 portion 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.

[0126] 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 100 wt %. The average particle size of the solid particles contained in the purified tail gas is in the range of 1 μm-10 mm.

[0127] According to this embodiment, the technical effects are detailed in Tables 1 to 3.

[0128] Example 2

[0129] The same as Example 1, except that the heavy hydrocarbon is paraffin-based crude oil, the final boiling point temperature is 800° C., the initial boiling point temperature is 20° C., and the API value of the heavy hydrocarbon is 39.

[0130] According to Example 2, most of the effects of Example 1 can still be achieved. However, due to the increased weight of heavy hydrocarbons, the cracking furnace tends to produce more coke in the convection section, radiant section, and quench heat exchanger. As a result, the operating cycle of the cracking furnace is shortened, the purge time of the cracking furnace before coking is prolonged, and the coking time is also prolonged. Compared with Example 1, the improvement in coking effect is slightly reduced. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0131] Example 3

[0132] The same as Example 1, except that the heavy hydrocarbons are heated to a temperature of 350° C. before passing through the gas-liquid separation device.

[0133] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0134] Example 4

[0135] 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.

[0136] According to Example 4, most of the effects of Example 1 can still be achieved. However, due to the higher operating temperature of the gas-liquid separation device and the higher gasification rate, some colloid is entrained in the gaseous material, coking is accelerated in the radiant section, the cracking furnace operating cycle is shortened, and purge and coking are slightly increased. The technical effects of this embodiment are detailed in Tables 1-3.

[0137] Example 5

[0138] The difference from Example 1 is that the operating temperature of the radiant section furnace tube pyrolysis is 820° C. and the operating pressure at the outlet of the radiant section furnace tube is 0.1 MPaG. The technical effects of this example are detailed in Tables 1 to 3.

[0139] Example 6

[0140] This embodiment is the same as Example 1, except that the air, after being heated in the convection section of the cracking furnace or by an external heater, has a temperature of 550°C, a pressure of 0.3 MPaG, and an inlet linear velocity of 15 m / s; and the steam, after being heated in the convection section of the cracking furnace or by an external heater, has a temperature of 550°C, a pressure of 0.3 MPaG, and an inlet linear velocity of 15 m / s. The technical effects of this embodiment are detailed in Tables 1-3.

[0141] Example 7

[0142] 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.

[0143] Example 8

[0144] The same as Example 1, except 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.

[0145] Example 9

[0146] This is the same as Example 1, except that the burners are evenly arranged at the bottom of the cracking furnace. Each burner has a central channel for receiving the charred exhaust gas returning to the furnace. The annular channel immediately outside the central channel serves as the air channel, and the annular channel immediately outside the air channel serves as the fuel gas channel. The technical effects of this example are detailed in Tables 1-3.

[0147] Example 10

[0148] This is the same as Example 1, except that the charred tail gas is transported through a main charred tail gas pipeline and then transported to the charred burners through multiple branch pipelines provided on the main charred tail gas pipeline. The number of these branch pipelines matches the number of burners. The technical effects of this example are detailed in Tables 1-3.

[0149] Example 11

[0150] The same as Example 1, except 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.

[0151] Example 12

[0152] This is the same as Example 1, except that the charred tail gas delivered to the charred burner located at the bottom of the furnace accounts for 80 wt% of the total mass of the charred tail gas, and the charred tail gas delivered to the charred burner located on the side wall of the furnace accounts for 20 wt% of the total mass of the charred tail gas. The technical effects of this example are detailed in Tables 1 to 3.

[0153] Example 13

[0154] The same as Example 1, except that the mass flow rate of the charred tail gas entering the single unit is 1000 kg / h. The technical effects of this example are detailed in Tables 1 to 3.

[0155] Example 14

[0156] This is the same as Example 1, except that the charred tail gas is separated from at least a portion of solid particles in a charring tank to obtain purified tail gas, which is then passed through 36 bottom charring burners and 18 sidewall burners into the furnace for combustion. The technical effects of this example are detailed in Tables 1-3.

[0157] Example 15

[0158] The same as Example 1, except that the separation is performed 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.

[0159] Example 16

[0160] 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.

[0161] Example 17

[0162] 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 1-3.

[0163] Example 18

[0164] The process is the same as that of Example 1, except that in step A), the steam temperature is 480° C., the pressure is 0.3 MPaG, and the inlet linear velocity is 30 m / s.

[0165] The technical effects of this embodiment are detailed in Tables 1 to 3.

[0166] Example 19

[0167] 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.

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

[0169] Example 20

[0170] The same as Example 1, except that before step 3) starts, the gas phase material is stopped from being transported to the radiation section furnace tube.

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

[0172] Example 21

[0173] 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.

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

[0175] Example 22

[0176] The same as embodiment 1, except that step 3) starts after step B) is completed.

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

[0178] Example 23

[0179] This is the same as Example 1, except that the API value of the heavy hydrocarbons is 35. Due to the heavy crude oil, the risk of coking increases in the convection and radiant sections, resulting in greater coke production during operation. This shortens the operating cycle, increases the coking time, and increases the amount of coke produced. This increases the risk of burner clogging and the impact on the thermal field within the furnace when the coke is returned to the furnace for burning. The technical effects of this example are detailed in Tables 1-3.

[0180] Example 24

[0181] This is the same as Example 1, except that the air is heated to 500°C in the convection section of the cracking furnace or by an external heater, and the steam is heated to 500°C in the convection section of the cracking furnace or by an external heater. The initial temperatures of the air and steam entering the radiant tubes are relatively low, increasing the burner load. Furthermore, the initial reaction rate of the air and steam within the tubes is slowed, reducing the decoking efficiency in the front section of the radiant tubes. The technical effects of this example are detailed in Tables 1-3.

[0182] Example 25

[0183] 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 installed 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 air flow 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 air flow will also impact the lining and furnace tubes of the furnace, causing damage to the equipment. 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 char gas in 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.

[0184] Example 26

[0185] This is the same as Example 1, except that the solid particle content of the purified exhaust gas is 40 mg / Nm³, based on the total weight of the purified exhaust gas being 100 wt%. Because the purified exhaust gas is not properly separated in the cyclone separator, the charred exhaust gas carried into the charred burner contains a high content of particulate matter. Since fuel gas nozzles generally have small apertures, this can easily cause clogging of other fuel gas nozzles in the burner. In this example, over 20% of the burner nozzles were clogged. The technical effects of this example are detailed in Tables 1-3.

[0186] Example 27

[0187] This is the same as Example 1, except that the solid particle content of the purified exhaust gas is 100 mg / Nm³, based on the total weight of the purified exhaust gas being 100 wt%. Because the purified exhaust gas is not well separated in the cyclone separator, the charred exhaust gas introduced into the charred burner contains a relatively high particle content of approximately 100 mg / Nm³. Since the fuel gas nozzles generally have a small aperture of 2-5 mm, this can easily cause the burner fuel gas nozzles to become clogged, resulting in sintering damage to the burner nozzles and uneven or insufficient heating within the furnace. In this example, over 30% of the burner nozzles were sintered and damaged. The technical effects of this example are detailed in Tables 1-3.

[0188] Example 28

[0189] This is the same as Example 1, except that the charred exhaust gas is directed through an annular channel rather than upward from the center of the burner. This results in the charred gas being too close to the burner, which can easily cause the fuel gas nozzle to extinguish. Furthermore, it does not effectively reduce the center flame temperature and has little effect on NOx reduction. The technical effects of this example are detailed in Tables 1-3.

[0190] Example 29

[0191] This is the same as Example 1, except that the charred tail gas from the sidewall charred burner accounts for 70wt% of the total mass of the charred tail gas. The irrational distribution of the charred tail gas between the bottom and sidewalls results in too little charred gas in the bottom burner and too much charred gas in the sidewall burner. Typically, the heat load of a single sidewall burner in a cracking furnace is much less than that of a bottom burner, resulting in a much greater processing capacity for the bottom burner than for the sidewall burner. The consequence of this uneven distribution is that the sidewall burner is at risk of flameout, and particles in the charred gas cannot be effectively burned in the sidewall burner. The technical effects of this embodiment are detailed in Tables 1-3.

[0192] Example 30

[0193] The same as Example 1, except that the mixed steam is not first obtained through the gas-liquid separator during the coking process, so it cannot 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.

[0194] Example 31

[0195] This is the same as Example 1, except that the air is heated to 350°C in the convection section of the cracking furnace or by an external heater, and the steam is heated to 350°C in the convection section of the cracking furnace or by an external heater. The initial temperatures of the air and steam entering the radiant tubes are too low, significantly increasing the burner load. Furthermore, the initial reaction rate of the air and steam within the tubes is slow, significantly reducing the decoking efficiency in the front section of the radiant tubes. This increases the coke burn time and utility consumption. The technical effects of this example are detailed in Tables 1-3.

[0196] Example 32

[0197] This is the same as Example 1, except that the steam inlet linear velocity is 90 m / s. This high linear velocity before the steam enters the radiant section furnace tubes causes vibration in the pipelines before entering the furnace tubes, resulting in excessive system pressure drop and increased consumption. Long-term vibration in the pipelines can easily cause stress tearing, leading to equipment damage. The technical effects of this example are detailed in Tables 1-3.

[0198] Example 33

[0199] This is the same as Example 1, except that the steam inlet linear velocity is 15 m / s. Because the steam linear velocity before entering the radiant section furnace tubes is too low, the Venturi is not throttled, resulting in uneven fluid distribution within the furnace tubes and localized overheating. This necessitates reducing the load and operating temperature of the cracking furnace, which prolongs the coke burning operation. The technical effects of this example are detailed in Tables 1-3.

[0200] Example 34

[0201] The same as Example 1, except that all 48 bottom burners are used as char burners. The technical effects of this example are detailed in Tables 1 to 3.

[0202] Example 35

[0203] The same as Example 1, except that all 96 side wall burners are used as char burners. The technical effects of this example are detailed in Tables 1 to 3.

[0204] Example 36

[0205] 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.

[0206] Comparative Example 1

[0207] 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.

[0208] Comparative Example 2

[0209] The same as Example 1, except that naphtha is used as the steam cracking raw material. The technical effects of this example are detailed in Tables 1 to 3.

[0210] Comparative Example 3

[0211] The same as Example 1, the difference is that the conventional method is used to return to the furnace, that is, only the burnt openings between the burners are returned to the furnace. The technical effects of this embodiment are detailed in Tables 1 to 3.

[0212] As shown in Tables 1 to 3, by comparing the data of Examples 1 to 35 (especially Example 1-22) with those of Comparative Examples 1 to 3, it can be seen that the charring method using heavy hydrocarbons mentioned in the present invention can reduce the average charring time by 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.

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 of claim 1, wherein in step 3), the air has a temperature of 500-650°C, a pressure of 0.2-0.4 MPaG, and an inlet linear velocity of 30-80 m / s, and the steam has a temperature of 500-650°C, a pressure of 0.2-0.4 MPaG, and an inlet linear velocity of 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 as 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.

Images