CN117965192A

CN117965192A - Cracking process

Info

Publication number: CN117965192A
Application number: CN202211306499.XA
Authority: CN
Inventors: 刘俊杰; 王国清; 杨士芳; 张利军; 李晓锋; 杨沙沙; 杜志国; 刘同举
Original assignee: Sinopec Beijing Chemical Research Institute Co ltd; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Chemical Research Institute Co ltd; China Petroleum and Chemical Corp
Priority date: 2022-10-25
Filing date: 2022-10-25
Publication date: 2024-05-03

Abstract

The invention relates to the field of cracking, and discloses a cracking method. The method is carried out in a cracking furnace, and the fuel gas in the cracking furnace comprises ammonia. The method can greatly reduce the emission of carbon dioxide and nitrogen oxides of the cracking device, can simultaneously meet the requirement of large-scale cracking furnaces, solves the problems that the cracking furnaces adopt fossil fuels for heating and the emission of carbon dioxide is overlarge, and realizes the low-carbon clean operation of the large-scale cracking device.

Description

Cracking process

Technical Field

The invention relates to the field of cracking, in particular to a cracking method.

Background

Unsaturated hydrocarbons of four and below carbon atoms are commonly referred to as light olefins, including organic chemical materials of high economic value such as ethylene, propylene, isobutylene, butadiene, and the like. With the economic progress of China, the demand of the organic chemical raw materials is increased year by year, and the increasing demand cannot be met even though the production scale of the low-carbon olefin is also increased year by year. A large amount of CO ₂,CO₂ can be generated in the production process, and a serious greenhouse effect can be brought, so that the development of the low-carbon olefin production technology has a wide application prospect.

In particular ethylene, the capacity of which is a sign of the national petrochemical industry level. The ethylene production device mainly depends on a cracking furnace, and the basic process is as follows: in the burner of the radiant section of the cracking furnace, fossil fuel is burnt in the presence of combustion-supporting gas to provide the energy required by the cracking reaction, so that the materials in the cracking furnace tube are heated, and the hydrocarbon cracking reaction is carried out at about 800-850 ℃ to change the hydrocarbon macromolecules into olefin micromolecules. In the convection section, the waste heat of the flue gas is used for preheating and vaporizing the raw materials, and simultaneously, the purpose of recovering heat is achieved through high-pressure steam in the steam drum. The cracking furnace is a large energy consumer in the whole ethylene process industry, and accounts for about 60% of the total energy consumption. Since the pyrolysis furnace fuel is usually methane, a large amount of CO ₂ is generated during combustion, and the pyrolysis furnace fuel is an important source of carbon tax in the field of petrochemical industry in the future.

CN202111100813.4 provides an electric heating ethylene cracking furnace device, which is basically characterized in that heat is provided for the cracking furnace in an electric heating mode, inert gas is heated in a radiation heat transfer mode, and then the waste heat of the inert gas is recovered by a convection section, and the inert gas is circulated, so that harmful pollutants such as greenhouse gas, nitrogen oxides (NOx) and the like are not generated. The heat-carrying gas in the furnace is recycled, and the thermal efficiency of the cracking furnace is up to more than 98%. However, the above scheme has the problems that only the electric heating resistance element is adopted for heating, and the high-grade heat energy utilization rate is low due to the limitation of the energy density of the electric heating element, the power consumption is huge, the economic benefit is poor, and the engineering feasibility is poor.

CN1145686C and CN113652246a provide a high-efficiency electric heating cracking furnace, the cracking furnace body is composed of a fixed furnace body and a movable furnace body, and the temperature in the furnace is flexibly and conveniently controlled and regulated by arranging a spacing bar. The cracking furnace has the characteristics of quick temperature rise and good heat preservation performance when in use, and is low-consumption and high-benefit; they also provide materials with good thermal insulation properties and are used in the high efficiency electric pyrolysis furnaces. The electric heating cracking furnace can quickly adjust the temperature in the furnace, but the heat flux density is small, so that the scale of the monomer cannot be enlarged, and the overall investment cost can be increased.

In 2021, the basf, sauter basic industries and linde company plans together develop a conceptual cracking furnace which uses renewable electric power to replace traditional fossil fuel gas, and enables the chemical industry to greatly reduce the emission of carbon dioxide. And the cooperative project aims to practically reduce carbon dioxide emissions by electrically driving the heating process.

CN202010514041.8 proposes an arrangement structure of ethylene cracking furnace burners, which is characterized in that under the condition that the bottom burner remains unchanged, the side wall burners are arranged in the middle of the side wall of the cracking furnace and are in a single row, and the bottom burner and the side wall burner can form long flame vertically upwards. The arrangement structure of the ethylene cracking furnace burners can effectively reduce the number of side wall burners, meets the requirements of the cracking furnace on combustion capacity, heat flux density distribution and NOx emission, and still uses fossil fuel.

The improvement of the cracking furnace in the prior art mainly aims at reducing the NOx emission and heat loss of the cracking furnace, improving the thermal efficiency of the cracking furnace and solving the problem of overhigh CO ₂ emission of the cracking furnace in the aspects of the structure, arrangement mode and the like of the burner of the cracking furnace. The electric heating cracking furnace is supplied with heat by using electric energy, but the internal temperature regulation of the cracking furnace is mainly realized by changing the diameter and the number of groups of heating wires, the mode is adopted to bring great inconvenience to daily operation, the temperature range which can be regulated integrally is limited, and the most critical is that the production scale of the pure electric heating furnace cannot be too large, and the overall investment cost is higher. Therefore, development of an ethylene cracking furnace with low-carbon fuel combustion heat supply, simple operation and controllable temperature is needed to meet the environmental protection requirement.

Disclosure of Invention

The invention aims to solve the problems in the prior art, and provides a cracking method and application, wherein the method can greatly reduce the emission of carbon dioxide and nitrogen oxides of a cracking device, can simultaneously meet the requirement of large-scale cracking furnaces, solves the problems that the cracking furnaces adopt fossil fuels for heating and the emission of carbon dioxide is overlarge, and realizes the low-carbon clean operation of the large-scale cracking device.

In order to achieve the above object, the present invention provides a cracking method, which is performed in a cracking furnace, wherein fuel gas of the cracking furnace comprises ammonia gas, and the volume concentration of the ammonia gas in the fuel gas is 0.1-100% by volume.

According to the technical scheme, ammonia is used as at least part of fuel gas, so that the emission of carbon dioxide of the cracking device can be reduced. Moreover, the mode can also meet the requirement of large-scale cracking furnace, and overcomes the difficulty of being unfavorable for large-scale in the electric heating mode. By adopting the preferred mode, if the cooling device is arranged, the generation of NOx can be reduced, and particularly the NOx emission can be further reduced by matching with the denitration device of the convection section. The scheme of the invention can realize low carbon and low NOx emission, and can effectively assist the development of the green petroleum industry.

Drawings

FIG. 1 is a schematic view of a pyrolysis furnace provided in a preferred embodiment of the present invention;

Fig. 2 is a schematic view of a burner structure at the bottom of a radiant section provided in a preferred embodiment of the present invention.

Description of the reference numerals

The device comprises a 1-convection section, a 2-heat exchange tube, a 3-selective catalytic reduction denitration device, a 4-cracking furnace tube, a 5-side wall burner, a 6-bottom burner, a 7-flue gas reflux device, an 8-steam injection device, a 9-radiation section, a 10-quenching waste boiler section, a 11-primary combustion-supporting gas inlet, a 12-primary gas inlet, a 13-secondary gas inlet, a 14-secondary combustion-supporting gas inlet and 15-refractory bricks.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

In a first aspect, the invention provides a cracking process carried out in a cracking furnace in which the combustion gas comprises ammonia and the concentration of ammonia in the combustion gas is in the range of 0.1 to 100% by volume (e.g. may be 0.1%, 1%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% by volume).

The inventor of the present invention found in the study that if ammonia gas is used as at least part of the fuel gas in the above manner, the emission of carbon dioxide from the pyrolysis device can be reduced; moreover, by adopting the mode, the requirement of large-scale cracking furnace can be met. It will be appreciated that cracking is typically carried out at higher temperatures, while ammonia is readily reacted under such conditions to form harmless nitrogen.

According to the present invention, preferably, the fuel gas further comprises other combustible gas selected from at least one of C1 to C4 alkane, hydrogen, C2 to C4 alkene. The other combustible gases may be provided by mixed dry gases from different refinery units.

According to the invention, the ammonia gas is preferably present in the fuel gas in a concentration of 5 to 99% by volume.

According to the present invention, the concentration of the other combustible gas in the fuel gas is preferably 0.01 to 98% by volume (for example, may be 0.01% by volume, 1% by volume, 10% by volume, 30% by volume, 50% by volume, 70% by volume, 80% by volume, 90% by volume, 95% by volume, 98% by volume, and any two values thereof form a range and a value within a range), and more preferably 1 to 95% by volume.

According to the present invention, it is preferable that the combustion supporting gas in the pyrolysis furnace is provided by at least one of air, oxygen-enriched air, pure oxygen and pyrolysis furnace flue gas. For example, the combustion-supporting gas may be provided by a mixture of air and pyrolysis furnace flue gas. It can be understood that the flue gas of the cracking furnace is the mixed gas obtained after the combustion of the gas for combustion and heat supply in the cracking furnace.

According to the present invention, the oxygen-enriched air preferably has an oxygen concentration of 22 to 60% by volume (for example, 22% by volume, 23% by volume, 25% by volume, 30% by volume, 40% by volume, 50% by volume, 60% by volume), and more preferably 23 to 40% by volume.

According to the present invention, the fuel gas is preferably a mixture of air and flue gas of the pyrolysis furnace, and the concentration of oxygen in the fuel gas in the mixture is 10 to 23 vol% (for example, 10 vol%, 12 vol%, 15 vol%, 18 vol%, 20 vol%, 22 vol%, 23 vol%).

According to the invention, preferably, the pyrolysis furnace comprises a convection section, a radiant section and a quench waste boiler section. In the radiation section, fuel is combusted to supply heat, raw materials are thermally cracked at a higher temperature, and meanwhile, high-temperature cracking furnace smoke is generated after the fuel is combusted; the high temperature pyrolysis furnace flue gas passes across and enters the convection section where the flue gas waste heat is used to preheat and gasify the feedstock, which then enters the radiant section for thermal cracking, and the excess heat can be used to preheat the boiler feed water and to superheat the high pressure steam produced by the quench boiler system. The quenching waste boiler section can recycle the energy of the high-temperature pyrolysis gas leaving the radiation section, so that the high-temperature pyrolysis gas is cooled and saturated ultrahigh-pressure steam is generated.

According to the invention, preferably, the number of radiating segments is plural, more preferably 2-5. Under the condition, the diameter and the length of the cracking furnace tube can be more conveniently adjusted, the ethylene production of a single radiation section can be obviously reduced, the highest temperature and the thermal field strength of a hearth are reduced, and therefore the generation of NOx (namely nitrogen oxides) is further reduced or even eliminated.

According to the invention, preferably, the number of convection sections is 1. It is possible to use a mode in which a plurality of radiation sections can share one convection section.

According to the invention, the bottom of the radiant section is preferably provided with a bottom burner.

According to the invention, the side wall of the radiant section is preferably provided with a side wall burner.

According to the present invention, it is preferable that the number of the bottom burners in one radiation section is 20 to 50 (for example, 20, 25, 30, 35, 40, 45, 50, and any two values thereof form a range and a value within the range).

According to the present invention, it is preferable that the number of the side wall burners in one radiation section is 50 to 90 (for example, 50, 60, 65, 70, 72, 75, 80, 85, 90, and any two values thereof form a range and a value within a range).

Preferably, the burner comprises a gas inlet and a combustion gas inlet.

By adopting the mode that the bottom and the side wall are provided with the burner, the bottom side is used for supplying heat in a combined way, the heating in the radiation section is more uniform, the cracking reaction is facilitated, and the generation of nitrogen oxides is reduced.

According to the present invention, it is preferable that the amount of the entering gas of the gas inlet and the combustion gas inlet of the burner of the bottom and the side wall is such that the amount of heat supply of the burner of the bottom is 30 to 100% (for example, may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%) with respect to the total amount of heat supply of the burner of the bottom and the heat supply of the burner of the side wall, more preferably 50 to 95%. Therefore, the temperature field distribution of the cracking furnace can be further controlled to be more uniform, and the generation of nitrogen oxides is reduced.

In general, the cracking of the raw materials requires that the partial temperature of the cracking reaction of the radiation section is controlled to be 1023-1123K, so that the heat supply is about 100-130MW relative to a cracking furnace with 10 ten thousand tons of ethylene per year.

According to the present invention, it is preferable that the gas inlet in the bottom burner is a multi-stage gas inlet. Ammonia gas has ignition delay effect (the combustion is not immediately started under the condition that the temperature is higher than the ignition temperature), and the heat release of the outlet of the burner is not very sufficient, so that the fuel gas is injected in a grading manner, and the combustion can fully release the heat. It will be appreciated that the composition of the incoming gas in each stage of gas inlets is generally uniform.

According to the invention, preferably, the gas inlet comprises a two-stage gas inlet; more preferably, the air intake of the first stage gas inlet is 25-45% by volume (e.g., may be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 43%, 45% by volume) of the total gas in the bottom burner, and the remaining gas is admitted from the second stage gas inlet. When the composition of the fuel gas and the total heat supply amount in unit time are determined, and the heat supply amount of the bottom side combustion is determined, the total fuel gas amount in the bottom burner in unit time can also be determined.

According to the invention, preferably, the gas inlet comprises a three-stage gas inlet; more preferably, the air intake amount of the first stage gas inlet is 15-30% by volume (for example, 15%, 18%, 20%, 22%, 25%, 28%, 30% by volume) of the total gas amount in the bottom burner, the air intake amount of the second stage gas inlet is 25-30% by volume of the total gas amount in the bottom burner, and the remaining gas is introduced from the third stage gas port.

According to the present invention, preferably, in the bottom burner, the combustion-supporting gas inlet is a multistage combustion-supporting gas inlet. The combustion-supporting gas inlet can also adopt a graded injection mode.

According to the present invention, it is preferable that the amounts of the auxiliary fuel gas and the fuel gas are such that the oxygen enrichment excess coefficient is 1.0 to 1.5, more preferably 1.1 to 1.3, in the pyrolysis furnace. The inventors of the present invention have further found that in the above-described case, not only can fuel combustion be further facilitated, combustion can be further ensured to be sufficiently performed, but also temperature distribution can be made more uniform. "oxygen enrichment excess" refers to the ratio of the actual amount of oxygen to the oxygen content required for combustion of the gas.

The amount of the combustion supporting gas inlet at the bottom stage is not particularly limited, as long as the oxygen enrichment excess coefficient in the cracking furnace can be satisfied and the fuel gas can be combusted. According to the present invention, preferably, the combustion-supporting gas inlet includes a two-stage combustion-supporting gas inlet; more preferably, the intake air amount of the first stage combustion-supporting gas inlet is 40-70% by volume (for example, 40%, 450%, 50%, 55%, 60%, 65%, 70% by volume) of the total combustion-supporting gas amount in the bottom burner, and the remaining combustion-supporting gas enters from the second stage combustion-supporting gas inlet.

Under the conditions of determining the air inflow of the fuel gas in unit time, determining the oxygen enrichment excess coefficient and determining the composition of the used fuel gas, the total oxygen demand and the total air inflow of the fuel gas can be obtained.

In the case where the fuel gas and the combustion supporting gas are injected in the plurality of stages as described above, in particular, in combination with the intake air amount at the time of the injection of each stage described above, it is also possible to further ensure that the heating amount ratio of the bottom and side wall burners satisfies the above-described preferred range. The gas inlet and the combustion gas inlet of the side burner may not be staged.

According to the invention, preferably, a cracking furnace tube is arranged in the radiant section. It can be appreciated that the raw materials of the cracking reaction are cracked in cracking furnace tubes in the radiant section; the combustion of the gas takes place in the furnace of the radiant section.

According to the invention, preferably, the cracking furnace tube is a single-pass furnace tube or a multi-pass furnace tube. It will be appreciated that the distinction between single pass and multiple pass is primarily whether the flow direction of the pyrolysis feedstock is changed, e.g., the multiple pass furnace tube may be U-shaped.

According to the present invention, preferably, the multi-pass furnace is a two-pass furnace, a four-pass furnace or a six-pass furnace.

According to the invention, preferably, the cracking furnace tube is in a 1-1 type or 2-1 type configuration. Taking a furnace tube of type 2-1 as an example, two numbers are connected by a short horizontal line in the configuration of the furnace tube, and the description is a two-pass furnace tube; wherein the first number "2" means that the first furnace tube has 2 furnace tubes with unchanged flow direction, i.e. the first furnace tube may be Y-shaped; the second number 1 refers to the number of furnace tubes with unchanged flow direction contained in the second-pass furnace tube being 1.

According to the invention, preferably, the cracking furnace tube is further provided with an enhanced heat transfer element. The heat transfer enhancing element may be any of a variety of commonly used elements such as twisted sheet tube heat transfer enhancing elements, spiral sheet inserts, twisted tape inserts, cross zigzag inserts, coil core inserts, wire wound porous bodies, spherical matrix inserts, and the like, to facilitate heat transfer. Different reinforced heat transfer elements can also be respectively added at different parts of the furnace tube. For example, the enhanced heat transfer elements may be twisted sheet tubes, and the twisted sheet tubes may be arranged intermittently over the cracking furnace tubes.

According to the invention, it is preferred that a cooling device is arranged in the furnace of the radiant section to provide cooling medium to the furnace. The cooling device may be a water vapor injection device.

According to the invention, preferably, the temperature reducing device is positioned at a height of 1000-1800K in the hearth when the radiation section is free of the temperature reducing device, so as to control the temperature in the hearth, preferably to control the temperature in the hearth to be in a range of 900-1400K. The temperature reducing device can be a steam injection nozzle, and the injection steam is used for controlling the temperature at the position of the height, so that the generation of NOx can be further reduced. The temperature reducing device is arranged at the position of the height of 1000-1800K in the hearth without the temperature reducing device, so that the temperature is controlled within the range through the temperature reducing device,

According to the invention, preferably, flue gas recirculation means are provided in the radiant section for recirculating the pyrolysis furnace flue gas for providing at least part of the combustion-supporting gas. So that the flue gas of the cracking furnace can be fully recycled, and the waste of discharged materials and heat is avoided.

It will be appreciated that the residence time of the pyrolysis feedstock in the pyrolysis furnace tubes of the radiant section is relatively short. Preferably, the residence time of the cleavage feed in the irradiation stage is from 20 to 600ms, more preferably from 50 to 400ms. The cracking feedstock may be ethane.

According to the invention, the convection section is preferably provided with a denitrification device for removal of nitrogen oxides, preferably a selective catalytic reduction denitrification device (i.e. SCR device). It will be appreciated that at high temperatures, and in particular in the preferred form of the invention, most of the ammonia gas is converted to nitrogen, but a small portion of the ammonia gas may still be formed and present in the high temperature flue gas. In this way, nitrogen oxides can be sufficiently removed.

The convection section can be provided with a heat exchange tube, the pyrolysis raw material flows in the heat exchange tube, and high-temperature pyrolysis furnace smoke exchanges heat with the pyrolysis raw material in the tube through the heat exchange tube, so that the pyrolysis raw material is heated, and the heat in the high-temperature pyrolysis furnace smoke is fully recovered.

According to the invention, the pyrolysis furnace preferably further comprises a gas preheater to preheat the combustion gases and/or before they are fed into the pyrolysis furnace. In this way, the combustibility and combustion stability of the fuel are further increased.

The present invention will be described in detail by examples.

Examples 1-3 were carried out in a pyrolysis furnace as shown in figure 1.

In fig. 1, 1 is a convection section, 2 is a heat exchange tube, 3 is a selective catalytic reduction denitration device, 4 is a cracking furnace tube, 5 is a side wall burner, 6 is a bottom burner, 7 is a flue gas reflux device, 8 is a steam injection device, 9 is a radiation section, 10 is a quenching waste boiler section, 11 is a primary combustion gas inlet, 12 is a primary gas inlet, 13 is a secondary gas inlet, 14 is a secondary combustion gas inlet, and 15 is refractory brick.

The pyrolysis furnace comprises a convection section 1, two radiant sections 9, and a quench waste pan section 10. The pyrolysis raw material firstly flows through the convection section 1, is preheated by the flue gas of the pyrolysis furnace, then enters the radiation section 9 for pyrolysis reaction, and then the pyrolysis gas obtained by pyrolysis flows through the quenching waste boiler section 10 and leaves the device. In one radiant section, the bottom of which is provided with 36 bottom burners 6 and the side wall is provided with 72 side wall burners 5 (only some of which are shown in the figure). A side wall burner 5 comprises a gas inlet and a combustion gas inlet. The radiation section is provided with a 2-1 two-pass cracking furnace tube, and the cracking furnace tube is discontinuously provided with twisted sheet tubes. When the cooling device is not arranged in the hearth of the radiation section, the generation amount of NO _X can be increased at a higher temperature, in order to reduce the emission of NO _X of the cracking furnace, a water vapor injection device 8 is arranged at the height of 1000-1800K of the temperature in the hearth of the radiation section without the cooling device so as to provide water for the hearth to cool, so that the temperature in the hearth is in the range of 900-1400K. A flue gas reflux device 7 is also arranged in the radiation section. The convection section is provided with a selective catalytic reduction denitration device 3, and the flue gas passes through the selective catalytic reduction denitration device 3 to remove nitrogen oxides therein.

As shown in fig. 2, a bottom burner 6 comprises 2 primary gas inlets 12 symmetrically distributed along the axis of the bottom burner, and 2 secondary gas inlets 13 symmetrically distributed along the axis of the bottom burner; the first-stage auxiliary gas inlet is positioned between the two first-stage gas inlets; two second-stage combustion-supporting gas inlets are distributed on two outer sides of the second-stage gas inlet.

In the examples below, the capacity of the cracker was about 10 ten thousand tons of ethylene per year, and the heat supply was therefore controlled at about 130MW. NO _X emissions (mg/m ³), in mg/m ³, per cubic meter of gas emitted, NO _X.

Example 1

The fuel gas of this example includes 80% by volume of ammonia and 20% by volume of hydrogen (i.e., the volume concentration of the other combustible gases in the fuel gas is 20% by volume excluding ammonia).

The fuel gas is supplied by air, wherein the concentration of oxygen is 23% by volume.

The amounts of the entering gases of the gas inlets and the combustion supporting gas inlets of the burners of the bottom and the side walls were controlled such that the heat supply amount of the burner of the bottom was 50% with respect to the total heat supply amount of the burner of the bottom and the heat supply amount of the burner of the side walls.

The air inflow of the first-stage gas inlet is controlled to be 25% by volume of the total gas in the bottom burner, and the residual gas enters from the second-stage gas inlet.

The air inflow of the first-stage combustion-supporting gas inlet is controlled to be 50% of the total combustion-supporting gas amount in the bottom combustor, the residual combustion-supporting gas enters from the second-stage combustion-supporting gas inlet, and the oxygen enrichment excess coefficient is controlled to be 1.1.

The residence time of the ethane cracking feed in the radiant section was controlled to be 400ms.

The cracking furnace has NO carbon dioxide emission, and the emission amount of NO _X is 45mg/m ³.

Example 2

The fuel gas of this example includes 20% by volume of ammonia, 75% by volume of hydrogen, and 5% by volume of CH ₄ (i.e., the volume concentration of the other combustible gases in the fuel gas is 80% by volume excluding ammonia).

The fuel gas is provided by oxygen-enriched air, wherein the concentration of oxygen is 35% by volume.

The amounts of the entering gases of the gas inlets and the combustion supporting gas inlets of the burners of the bottom and the side walls were controlled such that the heat supply amount of the burner of the bottom was 95% with respect to the total heat supply amount of the burner of the bottom and the heat supply amount of the burner of the side walls.

The air inflow of the first-stage gas inlet is controlled to be 45 volume percent of the total gas in the bottom burner, and the residual gas enters from the second-stage gas inlet.

The air inflow of the first-stage combustion-supporting gas inlet is controlled to be 65% by volume of the total combustion-supporting gas in the bottom combustor, the residual combustion-supporting gas enters from the second-stage combustion-supporting gas inlet, and the oxygen enrichment excess coefficient is controlled to be 1.3.

The residence time of ethane in the radiant section was controlled to be 400ms.

The carbon dioxide emission amount of the cracking furnace is 4mg/m ³,NO_X and the carbon dioxide emission amount of the cracking furnace is 30mg/m ³.

Example 3

The fuel gas of this example includes 50% by volume of ammonia, 25% by volume of CH ₄, and 25% by volume of C4 olefins (i.e., the volume concentration of the other combustible gases in the fuel gas is 50% by volume excluding ammonia).

The fuel gas is provided by a mixture of air and pyrolysis furnace flue gas, wherein the concentration of oxygen is 15% by volume.

The amounts of the entering gases of the gas inlets and the combustion supporting gas inlets of the burners of the bottom and the side walls were controlled so that the heat supply amount of the burner of the bottom was 75% with respect to the total heat supply amount of the burner of the bottom and the heat supply amount of the burner of the side walls.

The air inflow of the first-stage gas inlet is controlled to be 35% by volume of the total gas in the bottom burner, and the residual gas enters from the second-stage gas inlet.

The air inflow of the first-stage combustion-supporting gas inlet is controlled to be 60% of the total combustion-supporting gas amount in the bottom combustor, and the residual combustion-supporting gas enters from the second-stage combustion-supporting gas inlet, so that the oxygen enrichment excess coefficient is 1.2.

The residence time of ethane in the radiant section was controlled to be 400ms.

The carbon dioxide emission amount of the cracking furnace is 10mg/m ³,NO_X and the emission amount of the cracking furnace is 42mg/m ³.

Example 4

The same operating conditions as in example 1 were used, except that the cooling device located in the radiant section furnace was turned off.

The cracking furnace has NO carbon dioxide emission, and the emission amount of NO _X is 53mg/m ³.

Comparative example 1

The cracking was conducted in the same manner as in example 3 except that the fuel gas composition of this comparative example was 95% by volume of CH ₄, 5% by volume of H ₂, and the co-combustion gas was air, in which the oxygen concentration was 23% by volume. The carbon dioxide emission amount of the cracking furnace is 70mg/m ³,NO_X and the carbon dioxide emission amount of the cracking furnace is 100mg/m ³.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A cracking method, characterized in that the method is carried out in a cracking furnace, wherein fuel gas in the cracking furnace comprises ammonia gas, and the volume concentration of the ammonia gas in the fuel gas is 0.1-100% by volume.

2. The method of claim 1, wherein the fuel gas further comprises other combustible gases selected from at least one of C1-C4 alkanes, hydrogen, C2-C4 olefins;

preferably, the volume concentration of ammonia in the fuel gas is 5-99% by volume;

Preferably, the concentration of the other combustible gases in the fuel gas is 0.01 to 98% by volume, more preferably 1 to 95% by volume.

3. The method of claim 1 or 2, wherein the combustion gas in the pyrolysis furnace is provided by at least one of air, oxygen-enriched air, pure oxygen, and pyrolysis furnace flue gas;

preferably, the oxygen-enriched air has an oxygen concentration of 22 to 60 volume percent, more preferably 23 to 40 volume percent;

Preferably, the fuel gas is a mixed gas of air and flue gas of the cracking furnace, and the concentration of oxygen in the mixed gas is 10-23% by volume.

4. The method of claim 1, wherein the pyrolysis furnace comprises a convection section, a radiant section, and a quench waste section;

preferably, the number of radiating segments is plural, more preferably 2-5;

preferably, the number of convection sections is 1.

5. The method of claim 4, wherein the bottom of the radiant section is provided with a bottom burner;

Preferably, the side wall of the radiant section is provided with a side wall burner;

preferably, in one radiation section, the number of the bottom burners is 20-50;

preferably, in one radiation section, the number of the side wall burners is 50-90;

Preferably, the burner comprises a gas inlet and a combustion gas inlet;

Preferably, the amount of the entering gases of the gas inlet and the combustion gas inlet of the burner of the bottom and the side wall is such that the heat supply amount of the burner of the bottom is 30-100%, more preferably 50-95%, with respect to the total heat supply amount of the burner of the bottom and the burner of the side wall.

6. The method of claim 5, wherein in the bottom burner, the gas inlet is a multi-stage gas inlet;

Preferably, the gas inlet comprises a two-stage gas inlet; more preferably, the air inflow of the first-stage gas inlet is 25-45% by volume of the total gas in the bottom burner, and the residual gas enters from the second-stage gas inlet;

Preferably, the gas inlet comprises a tertiary gas inlet; more preferably, the air inflow of the first-stage gas inlet is 15-30% by volume of the total gas in the bottom burner, the air inflow of the second-stage gas inlet is 25-30% by volume of the total gas in the bottom burner, and the residual gas enters from the third-stage gas port.

7. The method of claim 5, wherein in the bottom burner, the combustion gas inlet is a multi-stage combustion gas inlet;

more preferably, the amount of gas supplied to the pyrolysis furnace is such that the oxygen enrichment excess is 1.0 to 1.5, and still more preferably 1.1 to 1.3.

8. The method of claim 4 or 5, wherein a cracking furnace tube is disposed in the radiant section;

preferably, the cracking furnace tube is a single-pass furnace tube or a multi-pass furnace tube;

preferably, the multi-pass furnace tube is a two-pass furnace tube, a four-pass furnace tube or a six-pass furnace tube;

preferably, the cracking furnace tube is in a 1-1 type or 2-1 type configuration;

Preferably, the cracking furnace tube is also provided with an enhanced heat transfer element.

9. A method according to claim 4 or 6, wherein a cooling device is provided in the furnace of the radiant section to provide cooling medium to the furnace;

preferably, the temperature reducing device is positioned at the height of 1000-1800K of the temperature in the hearth when the radiation section is free of the temperature reducing device, so as to control the temperature in the hearth, and preferably control the temperature in the hearth to be in the range of 900-1400K.

10. The method of claim 4, wherein a flue gas recirculation device is provided in the radiant section to recycle the pyrolysis furnace flue gas to provide at least a portion of the combustion-supporting gas.

11. A process according to claim 4 or 10, wherein the residence time of the cracking feedstock in the radiant section is 20-600ms, preferably 50-400ms.

12. A method according to claim 4 or 5, wherein the convection section is provided with a denitrification device for removal of nitrogen oxides, preferably a selective catalytic reduction denitrification device.

13. The method of claim 4 or 5, wherein the pyrolysis furnace further comprises a gas preheater to preheat the co-combustion gases and/or before feeding them into the pyrolysis furnace.