阅读说明：本技术 一种乙烯裂解炉和乙烯裂解方法 (Ethylene cracking furnace and ethylene cracking method ) 是由 何细藕 邵晨 赵永华 郭凡 于 2019-09-23 设计创作，主要内容包括：本发明属于石油化工领域,涉及一种乙烯裂解炉和乙烯裂解方法。该乙烯裂解炉包括：高压汽包、对流段、辐射段、急冷锅炉和燃烧器,所述辐射段内排布有多个辐射炉管组,每一辐射炉管组包括多支辐射炉管；所述对流段内排布有对流段换热管,所述对流段换热管为水平排布的多个换热管束；所述多个换热管束的布置方式使得对流段包括：上原料预热器、锅炉给水预热器、下原料预热器、一次稀释蒸汽过热器、二次稀释蒸汽过热器、上混合预热器、超高压蒸汽过热器和下混合预热器。提出了不同的对流段排布方案,解决了不同性质原料,特别是重质原料在对流段可能出现结焦的问题,同时更合理利用烟气的余热,减少换热面积,节省投资。(The invention belongs to the field of petrochemical industry, and relates to an ethylene cracking furnace and an ethylene cracking method. The ethylene cracking furnace comprises: the high-pressure steam drum comprises a high-pressure steam drum, a convection section, a radiation section, a quenching boiler and a burner, wherein a plurality of radiation furnace pipe groups are distributed in the radiation section, and each radiation furnace pipe group comprises a plurality of radiation furnace pipes; convection section heat exchange tubes are distributed in the convection section, and the convection section heat exchange tubes are a plurality of heat exchange tube bundles which are horizontally distributed; the plurality of heat exchange tube bundles are arranged such that the convection section comprises: go up raw materials preheater, boiler feed water preheater, lower raw materials preheater, once dilute steam superheater, secondary dilute steam superheater, upmix preheater, superhigh pressure steam superheater and lower mixing preheater. Different convection section arrangement schemes are provided, the problem that raw materials with different properties, particularly heavy raw materials are likely to be coked in a convection section is solved, meanwhile, the waste heat of the flue gas is more reasonably utilized, the heat exchange area is reduced, and the investment is saved.)

1. An ethylene cracking furnace, characterized in that, this ethylene cracking furnace includes: the high-pressure steam drum (1), the convection section (2), the radiation section (3), the quenching boiler (4) and the burner (5), wherein a plurality of radiation furnace pipe groups are distributed in the radiation section (3), and each radiation furnace pipe group comprises a plurality of radiation furnace pipes (6); convection section heat exchange tubes are distributed in the convection section (2), and the convection section heat exchange tubes are a plurality of heat exchange tube bundles which are horizontally distributed; the plurality of heat exchange tube bundles are arranged such that the convection section comprises: raw materials preheater, boiler feed water preheater, once dilute steam superheater, secondary dilute steam superheater, upmix preheater, superhigh pressure steam superheater and lower mixing preheater.

2. The ethylene cracking furnace of claim 1, wherein the primary dilution steam superheater and the secondary dilution steam superheater are arranged in series or in a partitioned arrangement; the primary dilution steam superheater is located above or below the secondary dilution steam superheater.

3. The ethylene cracking furnace of claim 1, wherein the primary dilution steam superheater inlet is provided with a primary dilution steam line communicating with outside of the battery compartment, and the secondary dilution steam superheater inlet is provided with a secondary dilution steam line communicating with outside of the battery compartment; alternatively, the first and second electrodes may be,

and a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

4. The ethylene cracking furnace of claim 1, wherein the feedstock preheater outlet line is combined with the primary dilution steam superheater outlet line and then connected to the upmix preheater;

an outlet pipeline of the upper mixing preheater and an outlet pipeline of the secondary dilution steam superheater are combined and then connected to the lower mixing preheater;

the primary dilution steam superheater is arranged above the upper mixing preheater;

the secondary dilution steam superheater is arranged above or below the ultrahigh pressure steam superheater.

5. The ethylene cracking furnace of claim 4, wherein the arrangement of the convection section is one of:

(1) the primary dilution steam superheater and the secondary dilution steam superheater are arranged adjacently up and down; the inlet of the primary dilution steam superheater is provided with a primary dilution steam pipeline communicated with the outside of the battery compartment, and the inlet of the secondary dilution steam superheater is provided with a secondary dilution steam pipeline communicated with the outside of the battery compartment;

(2) the primary dilution steam superheater and the secondary dilution steam superheater are arranged vertically but not adjacently; the inlet of the primary dilution steam superheater is provided with a primary dilution steam pipeline communicated with the outside of the battery compartment, and the inlet of the secondary dilution steam superheater is provided with a secondary dilution steam pipeline communicated with the outside of the battery compartment;

(3) the primary dilution steam superheater and the secondary dilution steam superheater are arranged adjacently up and down; the inlet of the primary dilution steam superheater is provided with a primary dilution steam pipeline communicated with the outside of the boundary area, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater;

(4) the primary dilution steam superheater and the secondary dilution steam superheater are arranged vertically but not adjacently; and a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

6. A method for ethylene cracking, characterized in that the method is carried out in an ethylene cracking furnace according to any one of claims 1-5, in which the feedstock and the dilution steam from outside are fed into a radiation section (3) for cracking reaction after preheating and mixing in a convection section (2); wherein, the primary dilution steam is mixed with the hydrocarbon from the raw material preheater after being superheated, the secondary dilution steam is mixed with the mixture of the hydrocarbon and the steam from the upper mixing preheater to realize the complete gasification and the superheating of the hydrocarbon, and finally the mixture of the steam and the hydrocarbon enters the radiation section after being further superheated in the lower mixing preheating section.

7. The ethylene cracking method of claim 6, wherein the diluting steam from the outside is directly fed into the primary diluting steam superheater and the secondary diluting steam superheater respectively to be mixed with the hydrocarbons and/or the hydrocarbons and the steam, or the diluting steam from the outside is fed into the primary diluting steam superheater and the secondary diluting steam superheater in sequence to be mixed with the hydrocarbons and/or the hydrocarbons and the steam to achieve complete gasification and superheating, and then is fed into the lower mixing preheater.

8. The ethylene cracking method of claim 6, wherein the raw hydrocarbons are mixed with the primary steam from the primary dilution steam superheater, and the resulting mixture is further mixed with the secondary steam from the secondary dilution steam superheater to achieve complete gasification and superheating, and then enters the lower mixing preheater.

9. The ethylene cracking method according to any one of claims 6 to 8, wherein the primary steam accounts for 10 to 90% of the total dilution steam; the secondary steam accounts for 10-90% of the total dilution steam.

10. The ethylene cracking method of claim 9, wherein the primary steam accounts for 20-60% of the total dilution steam; the secondary steam accounts for 40-80% of the total dilution steam.

Technical Field

The invention belongs to the field of petrochemical industry, and particularly relates to an ethylene cracking furnace and an ethylene cracking method.

Background

In an ethylene plant, the cracking furnace is the core plant (as shown in FIG. 1). Since the radiant section furnace tubes of the first radiant section vertical furnace tube structure was introduced by rums corporation in germany in 1964 with the development of cracking technology, several companies engaged in ethylene technology development invested a lot of capital and technical force to develop cracking technology.

In order to adapt to cracking of various raw materials with different properties and avoid coking in a convection section, companies for technical development research different injection modes of dilution steam according to the properties of different raw materials, particularly heavy raw materials.

The dilution steam injection methods adopted by most companies at present are: for cracking of gas or lighter feedstocks, dilution steam may be injected once in the convection section (engineering construction, etc., ethylene plant cracking feedstock adaptability operation discussion [ J ], ethylene industry); for heavier materials such as hydrogenated tail oil, dilution steam injection (CN87204914) can be used in the convection section. Different dilution steam injection modes directly influence the stable operation of the cracking furnace. If the injection mode is not proper, coking can be caused to occur in the convection section of the cracking furnace. And the convection section is coked, coke cannot be cleaned by an on-line coke-burning method, and the furnace can only be shut down.

Therefore, it is necessary to design a proper dilution steam injection manner to avoid coking in the convection section as much as possible.

Disclosure of Invention

The invention aims to provide an ethylene cracking furnace, which provides different convection section arrangement schemes, solves the problem that raw materials with different properties, particularly heavy raw materials can be coked in a convection section, simultaneously more reasonably utilizes the waste heat of flue gas, reduces the heat exchange area and saves the investment.

In order to achieve the above object, the present invention provides an ethylene cracking furnace comprising: the high-pressure steam drum comprises a high-pressure steam drum, a convection section, a radiation section, a quenching boiler and a burner, wherein a plurality of radiation furnace pipe groups are distributed in the radiation section, and each radiation furnace pipe group comprises a plurality of radiation furnace pipes; convection section heat exchange tubes are distributed in the convection section, and the convection section heat exchange tubes are a plurality of heat exchange tube bundles which are horizontally distributed; the plurality of heat exchange tube bundles are arranged such that the convection section comprises: raw materials preheater, boiler feed water preheater, once dilute steam superheater, secondary dilute steam superheater, upmix preheater, superhigh pressure steam superheater and lower mixing preheater. The relative arrangement mode of the primary dilution steam superheater and the secondary dilution steam superheater is not particularly limited, and the primary dilution steam superheater and the secondary dilution steam superheater can be arranged in series or in a separated manner; the primary dilution steam superheater may be located above or below the secondary dilution steam superheater.

In the present invention, the dilution steam mixed with the material is referred to as primary steam, and the dilution steam mixed with the material and primary steam mixture is referred to as secondary steam. The used primary steam and secondary steam can respectively enter two dilution steam superheating sections for superheating, or the primary steam firstly enters one dilution steam superheating section for superheating and then enters the other dilution steam superheating section for further superheating. Correspondingly, in the ethylene cracking furnace, the primary dilution steam superheater inlet is provided with a primary dilution steam pipeline communicated with the outside of the battery limits, and the secondary dilution steam superheater inlet is provided with a secondary dilution steam pipeline communicated with the outside of the battery limits; or a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

In the invention, preferably, the outlet pipeline of the raw material preheater and the outlet pipeline of the primary dilution steam superheater are combined and then connected to the upper mixing preheater; and an outlet pipeline of the upper mixing preheater and an outlet pipeline of the secondary dilution steam superheater are combined and then connected to the lower mixing preheater. The relative arrangement of the primary dilution steam superheater and the secondary dilution steam superheater and other convection section facilities is not particularly limited in the invention, and preferably, the primary dilution steam superheater is arranged above the upper mixing preheater; the secondary dilution steam superheater may be arranged above or below the extra-high pressure steam superheater.

Specifically, the arrangement of the convection section may be one of the following ways:

(1) the primary dilution steam superheater and the secondary dilution steam superheater are arranged adjacently up and down; the primary dilution steam superheater inlet is provided with a primary dilution steam pipeline communicated with the outside of the boundary area, and the secondary dilution steam superheater inlet is provided with a secondary dilution steam pipeline communicated with the outside of the boundary area.

(2) The primary dilution steam superheater and the secondary dilution steam superheater are not adjacently arranged up and down; the primary dilution steam superheater inlet is provided with a primary dilution steam pipeline communicated with the outside of the boundary area, and the secondary dilution steam superheater inlet is provided with a secondary dilution steam pipeline communicated with the outside of the boundary area.

(3) The primary dilution steam superheater and the secondary dilution steam superheater are not adjacently arranged up and down; and a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

(4) The primary dilution steam superheater and the secondary dilution steam superheater are arranged adjacently up and down; and a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

(5) In the above four modes, the mixture of the primary dilution steam, the secondary dilution steam and the hydrocarbon finally enters the radiation section through the lower mixing preheating section.

More specifically, the arrangement of the convection section may be one of the following ways:

(1) as shown in fig. 2, the convection section comprises from top to bottom: the system comprises an upper raw material preheater, a boiler feed water preheater, a lower raw material preheater, a primary dilution steam superheater, a secondary dilution steam superheater, an upper mixing preheater, an ultrahigh pressure steam superheater and a lower mixing preheater; the primary dilution steam superheater inlet is provided with a primary dilution steam pipeline communicated with the outside of the boundary area, and the secondary dilution steam superheater inlet is provided with a secondary dilution steam pipeline communicated with the outside of the boundary area.

(2) As shown in fig. 3, the convection section comprises from top to bottom: the system comprises an upper raw material preheater, a boiler feed water preheater, a lower raw material preheater, a primary dilution steam superheater, an upper mixing preheater, an ultrahigh pressure steam superheater, a secondary dilution steam superheater and a lower mixing preheater; the primary dilution steam superheater inlet is provided with a primary dilution steam pipeline communicated with the outside of the boundary area, and the secondary dilution steam superheater inlet is provided with a secondary dilution steam pipeline communicated with the outside of the boundary area.

(3) As shown in fig. 4, the convection section comprises from top to bottom: the system comprises an upper raw material preheater, a boiler feed water preheater, a lower raw material preheater, a primary dilution steam superheater, a secondary dilution steam superheater, an upper mixing preheater, an ultrahigh pressure steam superheater and a lower mixing preheater; and a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

(4) As shown in fig. 5, the convection section comprises from top to bottom: the system comprises an upper raw material preheater, a boiler feed water preheater, a lower raw material preheater, a primary dilution steam superheater, an upper mixing preheater, an ultrahigh pressure steam superheater, a secondary dilution steam superheater and a lower mixing preheater; and a primary dilution steam pipeline communicated with the outside of the boundary area is arranged at the inlet of the primary dilution steam superheater, and the inlet of the secondary dilution steam superheater is connected with the outlet of the primary dilution steam superheater.

The invention also provides an ethylene cracking method, which is carried out in the ethylene cracking furnace, wherein in the ethylene cracking furnace, the raw material and the dilution steam from outside enter a radiation section for cracking reaction after being preheated and mixed in a convection section; wherein, the primary steam is mixed with the hydrocarbon from the raw material preheater through heat, the secondary steam is mixed with the mixture of the hydrocarbon and the steam from the upper mixing preheater in the lower mixing preheater to realize the complete gasification and the superheating of the hydrocarbon, and finally the mixture of the steam and the hydrocarbon enters the radiation section through the lower mixing preheating section.

According to the invention, the diluting steam from the outside can directly enter the primary diluting steam superheater and the secondary diluting steam superheater respectively to be mixed with the hydrocarbon and/or the hydrocarbon and the steam, as shown in fig. 2 and 3, or the diluting steam from the outside can also enter the primary diluting steam superheater and the secondary diluting steam superheater in sequence to be mixed with the hydrocarbon and/or the hydrocarbon and the steam to realize complete gasification and superheating, and then enter the lower mixing preheater, as shown in fig. 4 and 5.

In the method of the invention, the raw hydrocarbon is mixed with primary steam from a primary dilution steam superheater, and the formed mixture is further mixed with secondary steam from a secondary dilution steam superheater to realize complete gasification and superheating, and then enters a lower mixing preheater.

According to the invention, the relative amounts of the primary steam and the secondary steam can be adjusted as desired. The primary steam can account for 10-90% of the total dilution steam; the secondary steam can account for 10-90% of the total dilution steam; preferably, the primary steam accounts for 20-60% of the total dilution steam; the secondary steam accounts for 40-80% of the total dilution steam.

Compared with the prior art, the invention has the beneficial effects that:

(1) the convection section scheme provided by the invention improves the applicability of the cracking furnace to different cracking raw materials, particularly the arrangement of the secondary dilution steam preheater is beneficial to cracking heavy raw materials and gasification of the raw materials, and effectively avoids coking caused by high temperature of the wall of the heat exchange tube when the raw materials are not completely gasified.

(2) The convection section scheme provided by the invention can fully utilize the waste heat of the flue gas to the maximum extent, and can make the heat utilization of the flue gas more reasonable by reasonably arranging the relative positions of the primary and secondary dilution steam preheaters in the whole convection section according to different cracking raw materials and different convection section temperature distribution curves. Under the condition of the same heat efficiency, the heat exchange area can be reduced, and the investment is saved.

(3) According to the scheme of the convection section provided by the invention, the heat exchange of the convection section is more reasonable and sufficient, the crossing temperature of materials can be improved, and the operation period of the cracking furnace is prolonged.

(4) The scheme of the convection section provided by the invention can effectively adjust and control the highest wall temperature and fin temperature of the heat exchange tube bundle in each preheater, and reduce the use of the heat exchange tube bundle of the convection section made of high material so as to save investment.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts throughout.

FIG. 1 is a schematic structural diagram of a conventional ethylene cracking furnace.

Fig. 2 shows the arrangement of the convection section in a first embodiment of the present invention. Wherein, the primary dilution steam superheater and the secondary dilution steam superheater are continuously arranged. And the primary dilution steam and the secondary dilution steam from the boundary area respectively enter a primary dilution steam superheater and a secondary dilution steam superheater for superheating.

Fig. 3 shows a convection section arrangement in a second embodiment of the present invention. Wherein, the primary dilution steam superheater and the secondary dilution steam superheater are arranged at intervals. And the primary dilution steam and the secondary dilution steam from the boundary area respectively enter a primary dilution steam superheater and a secondary dilution steam superheater for superheating.

Fig. 4 shows a convection section arrangement in a third embodiment of the present invention. Wherein, the primary dilution steam superheater and the secondary dilution steam superheater are continuously arranged. And (3) all the dilution steam from the boundary area enters a primary dilution steam superheater, then part of the dilution steam is mixed with the raw material, and the rest of the dilution steam enters a secondary dilution steam superheater for superheating.

Fig. 5 shows a convection section arrangement in a fourth embodiment of the present invention. Wherein, the primary dilution steam superheater and the secondary dilution steam superheater are arranged at intervals. And (3) all the dilution steam from the boundary area enters a primary dilution steam superheater, then part of the dilution steam is mixed with the raw material, and the rest of the dilution steam enters a secondary dilution steam superheater for superheating.

Fig. 6 is a schematic view of a convection section arrangement in the prior art.

Fig. 7 is a schematic view of another arrangement of convection sections of the prior art.

Description of reference numerals:

1. a high pressure steam drum; 2. a convection section; 3. a radiation section; 4. a quench boiler; 5. a burner; 6. a radiation furnace tube.

The system comprises an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a lower raw material preheater (LFPH), a primary dilution steam superheater (DSH-I), a secondary dilution steam superheater (DSH-II), an Upper Mixing Preheater (UMPH), an ultrahigh pressure Steam Superheater (SSH), an upper ultrahigh pressure steam superheater (USSH), a middle ultrahigh pressure steam superheater (MSSH), a lower ultrahigh pressure steam superheater (LSSH) and a Lower Mixing Preheater (LMPH).

Primary steam DS-1 and secondary steam DS-2.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.

In the following examples and comparative examples, a cracking furnace comprising a high-pressure steam drum 1, a convection section 2, a radiant section 3, a quench boiler 4 and a burner 5 was used as shown in FIG. 1, and a plurality of radiant tube groups each comprising a plurality of radiant tubes 6 were arranged in the radiant section 3.

Example 1

The convection section 2 employs a convection section arrangement as shown in fig. 2. The convection section is divided into eight sections from top to bottom, and the eight sections sequentially comprise: an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a lower raw material preheater (LFPH), a primary dilution steam superheater (DSH-I), a secondary dilution steam superheater (DSH-II), an Upper Mixing Preheater (UMPH), an ultrahigh pressure Steam Superheater (SSH), and a Lower Mixing Preheater (LMPH). The method comprises the following steps that dilution steam from a boundary area is divided into primary steam (DS-1) and secondary steam (DS-2), the primary steam (DS-1) is superheated in a primary dilution steam superheater (DSH-I) and then mixed with raw materials coming out of a lower raw material preheater (LFPH), an obtained oil-steam mixture enters an Upper Mixing Preheater (UMPH) to be superheated, the secondary steam (DS-2) is superheated in a secondary dilution steam superheater (DSH-II), the superheated dilution steam is mixed with a hydrocarbon mixture at an outlet of the Upper Mixing Preheater (UMPH), then enters a Lower Mixing Preheater (LMPH) to be superheated, and then goes to a radiation section 3 to react.

Example 2

The convection section 2 employs a convection section arrangement as shown in fig. 3. The convection section is divided into eight sections from top to bottom, and the eight sections sequentially comprise: an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a lower raw material preheater (LFPH), a primary dilution steam superheater (DSH-I), an Upper Mixing Preheater (UMPH), an ultra-high pressure Steam Superheater (SSH), a secondary dilution steam superheater (DSH-II) and a Lower Mixing Preheater (LMPH). The method comprises the following steps that dilution steam from a boundary area is divided into primary steam (DS-1) and secondary steam (DS-2), the primary steam (DS-1) is superheated in a primary dilution steam superheater (DSH-I) and then mixed with raw materials coming out of a lower raw material preheater (LFPH), an obtained oil-steam mixture enters an Upper Mixing Preheater (UMPH) to be superheated, the secondary steam (DS-2) is superheated in a secondary dilution steam superheater (DSH-II), the superheated dilution steam is mixed with a hydrocarbon mixture at an outlet of the Upper Mixing Preheater (UMPH), then enters a Lower Mixing Preheater (LMPH) to be superheated, and then goes to a radiation section 3 to react.

Example 3

The convection section 2 employs a convection section arrangement as shown in fig. 4. The convection section is divided into eight sections from top to bottom, and the eight sections sequentially comprise: an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a lower raw material preheater (LFPH), a primary dilution steam superheater (DSH-I), a secondary dilution steam superheater (DSH-II), an Upper Mixing Preheater (UMPH), an ultrahigh pressure Steam Superheater (SSH), and a Lower Mixing Preheater (LMPH). After the Dilution Steam (DS) from the boundary area is superheated in a primary dilution steam superheater (DSH-I), part of steam is mixed with raw materials coming out of a lower raw material preheater (LFPH), the obtained oil-steam mixture enters an Upper Mixing Preheater (UMPH) to be superheated together, the rest of steam is superheated in a secondary dilution steam superheater (DSH-II), the superheated dilution steam is mixed with a hydrocarbon mixture at the outlet of the Upper Mixing Preheater (UMPH), then enters a Lower Mixing Preheater (LMPH) to be superheated, and then goes to a radiation section 3 to be reacted.

Example 4

The convection section 2 employs a convection section arrangement as shown in fig. 5. The convection section is divided into eight sections from top to bottom, and the eight sections sequentially comprise: an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a lower raw material preheater (LFPH), a primary dilution steam superheater (DSH-I), an Upper Mixing Preheater (UMPH), an ultra-high pressure Steam Superheater (SSH), a secondary dilution steam superheater (DSH-II) and a Lower Mixing Preheater (LMPH). After the Dilution Steam (DS) from the boundary area is superheated in a primary dilution steam superheater (DSH-I), part of steam is mixed with raw materials coming out of a lower raw material preheater (LFPH), the obtained oil-steam mixture enters an Upper Mixing Preheater (UMPH) to be superheated together, the rest of steam is superheated in a secondary dilution steam superheater (DSH-II), the superheated dilution steam is mixed with a hydrocarbon mixture at the outlet of the Upper Mixing Preheater (UMPH), then enters a Lower Mixing Preheater (LMPH) to be superheated, and then goes to a radiation section 3 to be reacted.

Comparative example 1

The convection section 2 employs a convection section arrangement as shown in fig. 6. The convection section is divided into six sections from top to bottom, and the six sections sequentially comprise: the system comprises an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a primary dilution steam superheater (DSH-I), an Upper Mixing Preheater (UMPH), an ultrahigh pressure Steam Superheater (SSH) and a secondary dilution steam superheater (DSH-II). After the Dilution Steam (DS) from the boundary area is superheated in the primary dilution steam superheater (DSH-I), part of the steam is mixed with the raw material coming out of the upper raw material preheater (UFPH), the oil-steam mixture enters the Upper Mixing Preheater (UMPH) to be superheated, the rest of the steam is superheated in the secondary dilution steam superheater (DSH-II), and the superheated dilution steam is mixed with the hydrocarbon mixture at the outlet of the Upper Mixing Preheater (UMPH) and then goes to the radiation section 3 to be reacted.

Comparative example 2

The convection section 2 employs a convection section arrangement as shown in fig. 7. The convection section is divided into nine sections from top to bottom, and the nine sections sequentially comprise: the system comprises an upper raw material preheater (UFPH), a boiler feed water preheater (BWPH), a lower raw material preheater (LFPH), an Upper Mixing Preheater (UMPH), an upper ultrahigh pressure steam superheater (USSH), a middle ultrahigh pressure steam superheater (MSSH), a lower ultrahigh pressure steam superheater (LSSH), a primary lower mixing preheater (LMPH-I) and a secondary lower mixing preheater (LMPH-II). The raw material enters a lower raw material preheater (LFPH) through an upper raw material preheater (UFPH), then is mixed with Dilution Steam (DS) from a boundary region and enters an Upper Mixing Preheater (UMPH) for overheating, and a hydrocarbon mixture at the outlet of the Upper Mixing Preheater (UMPH) sequentially enters a primary lower mixing preheater (LMPH-I) and a secondary lower mixing preheater (LMPH-II) and then goes to a radiation section 3 for reaction.

The prior art shown in fig. 7 is a conventional convection section arrangement that is prone to coking due to non-optimized dilution steam entry and mixing with the feedstock. In the prior art as shown in fig. 6, although a primary dilution steam superheater and a secondary dilution steam superheater are provided. However, because the lower mixing preheater is not arranged, the materials of the secondary dilution steam superheater and the upper mixing preheater are directly mixed and then enter the radiation section, so that sufficient and uniform mixing and vaporization of the materials and the dilution steam cannot be guaranteed, and the risk of coking of the radiation section due to incomplete vaporization is increased. And, because the abundant schizolysis of radiation section needs higher material to span the temperature, and secondary dilution steam gets into the radiation section after directly mixing with the material in this mode, and the upmix preheater in the design and secondary dilution steam superheater exit temperature all are higher, all need adopt high material tube bank, have reduced production economy, and have reduced the controllability of secondary steam quantity, and the flexibility of pyrolysis furnace operation has received the restriction.

In the present invention, as shown in fig. 2 to 5, the primary steam is superheated in the primary dilution steam superheater and then mixed with the preheated raw material. After being superheated in a secondary dilution steam superheater, the secondary steam is mixed with a superheated material and steam mixture and then enters a Lower Mixing Preheater (LMPH) for superheating. Such convection current section arranges, can help the gasification of raw materials, when effectively avoiding the raw materials not totally gasified yet, because the heat exchange tube wall temperature is high and lead to the coking, realizes utilizing the purpose that dilution steam superheated section balanced convection current section temperature distribution. Moreover, the convection section heat exchange tube bundle made of high materials can be avoided, and the investment is further saved.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.