Pyrolysis furnace with new type radiant tubes arrangement and method of its operation and usage

Abstract

The present invention provides a pyrolysis furnace with new type radiant tubes arrangement and method of its operation and usage. The first pass tubes and second pass tubes of radiant tubes of pyrolysis furnace according to the present invention are located at two parallel planes respectively, the projection of second pass tube of radiant tubes in each group is corresponding to the center location of projection connecting line of two first pass tubes adjacent therewith. The present invention can also employ top burners and bottom burners; the inlet of crossover section is located at middle-upper portion of radiant section wall. The present invention has the feature of uniform heat conduction, high effectiveness, flexible and simple operation and control, and small investment, it is suitable for cracking reaction of hydrocarbons feedstock.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a pyrolysis furnace and method of its operation and usage, specially relates to a pyrolysis furnace with new type radiant tubes arrangement for high temperature cracking reaction of Hydrocarbons, and the method of its operation and usage.

[0003] 2. Description of the Prior Art

[0004] As is known to all, the pyrolysis reaction of Hydrocarbons is main means for production of very important industrial raw materials such as ethylene, propylene, etc. Even a little improvement occurs in this field, it can bring about giant economic and social benefits. Pyrolysis furnace is the main equipment for performing high temperature cracking, therefore, nearly all chief Hydrocarbons and petro-chemical companies of the world pay great attention to and not spare to make huge amount of investment for modification of pyrolysis furnaces.

[0005] As is under stood to person skilled in the art that the structure, and uniform heat receipt of radiant tubes are important factors affecting the cracking reaction result. The radiant section of traditional vertical pyrolysis furnace in most cases employ single row tubes to ensure uniform heat receipt of radiant tubes. There are also some companies, which for the purpose to obtain larger productivity of single furnace under lower investment EMPLOY double row tubes, and for combined feature of both arrangements, EMPLOY staggered row tubes. Abovementioned content is available from reference to <<The technology of ethylene>>, by Chen Bing (Chemical industrial pub house, 1997, 1st ed, chap. 4) <<The theory and technology of pyrolysis for the Hydrocarbons chemistry>> by Zhou Ren-juin (chemical industrial pub. house, 1981, 1st ed, chap 6) and <<Technique of device for ethylene>> by Wong Song-hang (Hydrocarbons chemical industrial pub. house, China, 1994, 1st ed chap 6).

[0006] The radiant tubes employing single row arrangement in radiant section receive double-wall radiation; they have the most uniform heat receiving and best heat conducting effect. But the disadvantage is that in same area the number of tubes capable to be arranged is minimum, the productivity of specific area is low. Under this condition of single row arrangement, in order to meet the requirement of magnification of pyrolysis furnace, it needs to extend the length of every radiant tubes or the length of radiant section, an inexorable result is that we have to greatly increase the height and length of radiant section and meet the more severe requirement for uniform heat supply by burners in radiant section. At same time extremely long radiant tube makes the engineering problems complicated. Therefore, the use of single row arrangement structure significantly limits the productivity of pyrolysis furnace.

[0007] Although the use of double row of radiant tubes arrangement can increase the productivity by 70%, but the mutual overlap between tubes of double row seriously affects heat conductivity of heater wall from its radiation, this results in worse conductive effect from radiation, at the same time, non-uniform heat receipt of radiant tubes brings about disadvantages to cracking selectivity, employ cycle, and lifetime of radiant tubes.

[0008] Although the use of staggered row arrangement can partly increase productivity and uniformity of heat receipt, but in order to ensure uniformity of radiant conduction, the distance between adjacent radiant tubes must be not lower than 1.8 times of outer diameter thereof, the space saved within furnace chamber is limited. Besides, in order to avoid mutual cross-link of radiant tube bends in adjacent groups and manifolds in lower portion of furnace chamber, we have to locate the bends of adjacent groups and manifolds at different heights or different planes, this leads to two by-effects: at one hand, the radiant tubes located at different heights, having different overall lengths in various groups, thus retained time and severity of feedstock is different in various groups, this makes certain limitation to the optimization controlling. At the other hand, the bends and manifolds located at different planes gives significant affectation to stress of all radiant tubes, which easy to cause deformation of radiant tubes. Moreover, this leads to complicated design of radiant tube bends, multiple types-kinds, bad interchangeability, high difficulty in mounting and increased investment.

[0009] FIG. 6 shows an arrangement of prior art of two pass branched radiant tubes 7 with different diameters of type 2-1 in radiant section 3, wherein the first pass and second pass tubes are located in a same plane, this is a single row arrangement. It can be seen that although the tubes uniformly receive heat, but not so many tubes are arranged in radiant section, the space utilization is not high, as well as the arrangement of tubes is not symmetrical and tube lengths are not the same, this leads to different working condition of cracking process in various tubes, and thus the cracking effect is affected.

[0010] In addition, high temperature condition of cracking reaction is achieved by heat supply from burners to radiant tubes in the radiant section. In accordance with the mounting location in the radiant section, the burners are divided into bottom burners, wall burners and top burners.

[0011] In U.S. Pat. No. 4,361,478 the company LINDE discloses a pyrolysis furnace entirely employing heat supply manner by means of wall burners. The pyrolysis furnace entirely employing heat supply manner by means of wall burners has the feature of uniform temperature distribution in furnace chamber, small width of furnace chamber, etc, but too much burners are located in whole pyrolysis furnace, distribution piping of fuel is complicated, investment is large, and the employ and maintenance in practice is an expensive matter.

[0012] In U.S. Pat. No. 4,999,089 the Japanese company MITSUI discloses a pyrolysis furnace entirely employing heat supply manner by means of top burners. At this manner, the structure of radiant section is irregular, the form of fuel current in furnace chamber is complicated, more over, the heater wall at radiant section is tilted, under the condition of high temperature employ, the isolation lining materials of heater wall are easy to be broken-up in employ, it results in great amount of repair. Besides since the outlet of fuel gas is located at bottom portion of radiant section, the high-powered extraction fan is need to provided for back current of fuel gas in radiant section, such furnace has increased cost and energy consumption.

[0013] In U.S. Pat. No. 5,151,158 the company S & W describes a pyrolysis furnace with entire heat supply from bottom burners, it wholly use heat supply from bottom burners, it is advantageous in simple employ, and minimum amount of maintenance. But the requirement to burners is relative high, when the height of furnace chamber at radiant section is higher, it is, necessary to have some burners of special design to meet uniform temperature requirement in furnace chamber. These burners are complex in manufacture and expensive.

[0014] In U.S. Pat. No. 4,342,642 the company LUMMUS discloses a pyrolysis furnace with bottom-wall combined heat supply manner, although this kind of heat supply manner can obtain uniform temperature in furnace chamber by means of conventional bottom or wall burners, but the use of wall burners is still needed, thus such problems, as complexity of distribution piping, large investment and high cost of employ and maintenance, etc, are still present in.

[0015] Abovementioned pyrolysis furnace of prior art generally comprising: a convection section, used for preheating the hydrocarbons feed stock; a radiant section, used for high temperature cracking hydrocarbons feedstock; and crossover section, connected between the convection section and radiant section. A typical pyrolysis furnace with bottom burning manner is shown in FIG. 5, wherein bottom burners 8 and multiple groups of radiant tubes 7 are arranged in radiant section 3; the convection section is located above the radiant section and axially shifted therewith, wherein multiple groups of convection tubes 1 are arranged; a crossover section 6 is passed horizontally from top portion of radiant section to connect with bottom portion of convection section. The above mentioned pyrolysis furnace of prior art has greater overall height, it increases design and technology difficulty and results in larger amount of capital expenditure at same time.

[0016] To Sum up, all the furnaces of prior art have their advantages, but also have many shortages and problems. Therefore, it is necessary to seek for a pyrolysis furnace of new type with excellent compositive properties, to overcome above described shortages.

SUMMARY OF THE INVENTION

[0017] The object of the present invention is to provide a pyrolysis furnace with new type radiant tubes arrangement in radiant section, which has the feature of simple employ, excellent heat conduction, small investment, easy maintenance, and flexible control.

[0018] In order to realize above object, the inventor has carried though a great deal of careful investigation and found that employ of new type radiant tubes arrangement design in radiant section, which never has been used by others, is effective means to solve abovementioned problems.

[0019] The present invention provides a pyrolysis furnace with new type radiant tubes arrangement, the pyrolysis furnace comprising:

[0020] a) vertically arranged radiant section, in which burners and multiple groups of radiant tubes are arranged for high temperature cracking hydrocarbons feedstock;

[0021] b) vertically arranged convection section, located above the radiant section and axially shifted therewith, in said convection section multiple groups of convection tubes are arranged for preheating the hydrocarbons feedstock;

[0022] c) horizontally arranged crossover section, connected between said radiant section and said convection section;

[0023] Characterized in that

[0024] said multiple groups radiant tubes are two pass tubes with different diameters, the first pass tubes and second pass tubes are located at two parallel planes, more over, the projection of each second pass tube is corresponding to the center line of projection connecting line of two first pass tubes, adjacent therewith, the structure of each first pass and second pass tube is the same.

[0025] In order to resolve the problem of arrangement and uniform heat receipt of radiant tubes, said radiant tubes may be two pass non-branched tubes with different diameters (type 1-1) or two pass branched tubes with different diameters (type 2-1, 4-1), wherein the two pass branched tubes with different diameters (type 2-1) are particularly preferred. Wherein the pitch between two adjacent radiant tubes in said same plane is 1.8˜6.0 times of outer diameter of the radiant tubes, preferably, 1.8˜4.2 times, more preferably, 2.0˜2.8 times, the distance between the planes where said first pass tubes and second pass tubes are located is 100˜600 mm, preferably, 200˜500 mm, most preferably, 300˜400 mm.

[0026] The pyrolysis furnace of this invention may also employ a new type heat supply manner, wherein top burners and bottom burners are simultaneously arranged in said radiant section, and said crossover section is extended from middle-upper portion of radiant section wall, and connected to bottom portion of convection section.

[0027] A further object of present invention is to provide method and usage of high temperature cracking hydrocarbons feedstock by means of said pyrolysis furnace, including: preheating hydrocarbons feedstock and dilution steam mixture, etc, in convection tubes by means of fuel gas came from radiant section; high temperature cracking preheated hydrocarbons feedstock, wherein maintaining the heat supply ability of bottom burners constant, regulating the heat supply ability of top burners within a small range to satisfy different temperature requirement for cracking different kinds of hydrocarbons feedstock.

BRIEF DESCRIPTION OF DRAWINGS

[0028] The present invention will be better understood through describing in reference to the following drawings, in which:

[0029] FIG. 1 is a diagrammatic elevation view of a new type pyrolysis furnace according to the present invention;

[0030] FIG. 2 is a top view of radiant section of pyrolysis furnace according to the present invention, taking as an example, the radiant tubes are type 2-1;

[0031] FIG. 3 is an elevation view of FIG. 2 wherein two groups of radiant tubes are shown;

[0032] FIG. 4 is a side view of FIG. 2;

[0033] FIG. 5 is a diagrammatic view of a typical pyrolysis furnace employing bottom burners heat supply in the prior art;

[0034] FIG. 6 is a diagrammatic top view and elevation view of a single row arrangement of radiant tubes in a pyrolysis furnace in the prior art.

DETALLED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] As FIG. 1 shows, the new type pyrolysis furnace of this invention comprising radiant section 3; bottom burners 8, arranged in radiant section 3; multiple groups of two pass non-branched tubes with different diameters 7 (type 1-1) or two pass branched tubes with different diameters 7 (type 2-1, 4-1), vertically arranged in radiant section; wherein, tubes with different diameters means that the first pass tube and second pass tube in two pass tubes has different diameter, but two or four first pass tubes in two pass tubes type 2-1, 4-1 should have same diameter; convection section 2, shifted from radiant section 3; multiple groups of convection tubes 1, horizontally arranged in convection section 2; crossover section 6, horizontally arranged between radian section 3 and convection section 2;

[0036] The feedstock for cracking is introduced from the convection tubes 1 in convection section of furnace through the crossover tube 5 of convection tubes 1 into radiant tubes 7, then successively pass through the first pass tubes (1 tube, 2 tubes or 4 tubes) of radiant tubes 7, second pass tube (1 tube), at last pass from outlet of second pass tube of radiant tubes 7 into Transfer Line Exchange(TLE) 4.

[0037] In order to resolve the problem of radiant tube construction, arrangement, and uniform heat receipt, said radiant tubes may be two pass non-branched tubes with different diameters (type 1-1) or two pass branched tubes with different diameters (type 2-1), wherein the two pass branched tubes with different diameters (type 2-1) are particularly preferred.

[0038] The first pass tubes and second pass tubes of various groups are located at two parallel planes respectively, and the projection of each second pass tubes is corresponding to the center location of projection connecting line of two first pass tubes, adjacent there with, and the structure of each first tube and second tube is the same respectively, wherein the pitch between two adjacent radiant tubes in said same plane is 1.8˜6.0 times of outer diameter of the radiant tubes, preferably, 1.8˜4.2 times, more preferably, 2.0˜2.8 times; the distance between first pass tubes and second pass tubes of each group is 100˜600 mm, preferably, 200˜500 mm, most preferably, 300˜400 mm.

[0039] Because the present invention employs new type arrangement of radiant tubes, so as to make the pitch between two adjacent radiant tubes in same plane to be just right, the bends of radiant tubes of radiant section in various groups and manifold are parallel each other without cross link, this has no influence on radiant heat conduction of radiant tubes in various groups, simultaneously, the form and weight of bends of radiant tubes in various groups and manifold are fully the same, these components have high versatility, and are simple for manufacture and maintenance; the overall length of radiant tubes of radiant section in various groups are fully the same, the residence time and pressure drop of feedstock are fully the same, which is easy to optimization of employ and control; the weight of radiant tubes of radiant section in various groups is fully the same, this makes the balance and suspension system easy to be arranged and regulated.

[0040] Because this arrangement can reduce the length of pyrolysis furnace, it is suitable to various traditional or new type TLEs.

[0041] In pyrolysis furnace, according to the present invention, top burners 9 can also be added in radiant section, as shown in FIG. 1. The location of the crossover section 6 can be determined by the top/bottom burners' heat supply ratio R of different pyrolysis furnaces. When R varies in a range of 1:9˜7:3, the top wall of crossover section is located under the top wall of radiant section, its distance H is 10%˜50% of total height of radiant section wall, preferably, R varies in a range of 2:8˜6:4, H is 10%˜40% of total height of radiant section wall; more preferably, R varies in a range of 2.5: 7.5˜5:5, H is 15%˜40% of total height of radiant section wall, most preferably, R varies in a range of 3:7˜4:6, H is 20%˜40% of total height of radiant section wall.

[0042] In a pyrolysis furnace according to a preferred embodiment of this invention, said top burners and bottom burners can be used to supply all heat need for high temperature cracking top burners and bottom burners may be, preferably combined oil-gas burners.

[0043] According to a form of modification of this invention, we can maintain the heat supply ability of bottom burners constant, while regulate the heat supply ability of top burners at a small range, so as to satisfy the requirement need for high temperature cracking of different kinds of feedstock.

[0044] According to a preferred embodiment of this invention, said pyrolysis furnace can employ top burners and bottom burners of same amount. The top or bottom burners may be arranged symmetrically about centerline of top or bottom portion, the ratio of numbers of top/bottom burners is equal to, and corresponding to one another at top and bottom portions, moreover, the top/bottom burners heat supply ratio R can be controlled by controlling the top/bottom burners fuel feeding ratio.

[0045] A pyrolysis furnace according to a preferred embodiment of this invention, wherein the used top burners and bottom burners may be burners of various kinds, as known to a person skilled in the art. In order to reduce cost, preferably employ conventional burners.

[0046] Because the top burners employ both liquid and gas fuels, or may be an oil-gas combined burners, as compared with the wall burners heat supply or bottom-wall combined heat supply manners, the present invention can reduce the number of burners, so as to reduce the investment and simplify the structure of pyrolysis furnace; moreover, the present invention can fully are the conventional burners, as top and bottom burners, which can be produced in our country, and is inexpensive, and simple in employ and maintenance.

[0047] Besides, due to employ of top and bottom burners combined heat supply manner, the temperature distribution is relatively uniform, at the same time the top/bottom burners heat supply ratio R can be adjusted in period of design according to the structure requirements, thus the design flexibility is greatly increased; in addition, employ of top and bottom burners combined heat supply manner of this invention, the outlet of fuel gas of cross over section, which is located at top portion of radiant section of traditional art, is shifted down to middle-upper portion of radiant section, this not bring about negative influence on the cracking effect of pyrolysis furnace, but makes the height of convection section 2 to shift down, so that the overall height of pyrolysis furnace may be lowered (by 3˜6 m in average, the particular height is controlled by top/bottom burners heat supply ratio R). As a result, the center of gravity of whole pyrolysis furnace is dropped down, this reduce the capital construction cost. Moreover, in practical employ, according to the need for different outlet temperature of various fuel kinds, it can maintain the heat supply ability of bottom burners as constant, as well as regulate the heat supply ability of top burners in a small range, to satisfy respective condition so as to greatly increase the flexibility in practical employ.

[0048] Here after, the present invention will be described in more detail by way of examples, however, these examples are not intended to refer as limitations for this invention, For those skilled in the art, various changes and modifications can be made, depending the inspire, obtained from detailed description of present invention, for example, the pyrolysis furnace employing the radiant tubes arrangement manner of this invention, but the radiant tubes are back branched tubes; also for example, pyrolysis furnace employing a common convection section for two or more radiant sections. All these apparent changes are within the scope of the present invention.

EXAMPLE 1

[0049] A pyrolysis furnace has the yield of ethylene of 100 kiloton per year. Said pyrolysis furnace comprising: a radiant section with furnace chamber height of about 17 m; a convection section shifted from radiant section, with height about 15 m; a cross over section, horizontally arranged and extended between said radiant and convection sections, the upper edge of outlet of crossover section is located about 6 m below from the top portion of furnace chamber; 24 top burners, arranged symmetrically about the center line of top portion, and 24 bottom burners arranged symmetrically about the center line of bottom portion; multiple groups of convection tubes, horizontally arranged in convection section, and 48 groups of radiant tubes (type 2-1), vertically arranged in radiant section. Because the location of crossover section is shifted down about 6 m, the over all height of furnace is cut down about 6 m, where as the former pyrolysis furnace of the same scale, employing wall and bottom burners combined heat supply manner need to comprise 24 bottom burners and 48 wall burners.

[0050] If the furnace employ former staggered row arrangement of radiant tubes, by only possibility is to arrange 48 groups of radiant tubes (type 2-1), the bends of adjacent groups and manifolds are located in different heights, as well as in different planes, the distance between is 1.8 times of outer diameter of radiant tubes, the length of of furnace chamber is about 20 m. In a reconstruction and innovation program design, the radiant tubes are arranged by the arrangement manner of the present invention, all the first pass tubes are located at one plane, all the second pass tubes are located at another plane, the distance between two planes is 320 mm, when the distance between first pass tubes is 2.4 times of outer diameter thereof, and the distance between second pass tubes is 3.5 times of outer diameter thereof, 64 groups of radiant tubes (type 2-1) can be arranged in the same furnace chamber, this increases the productivity by 33%;

[0051] The radiant tubes are arranged by the arrangement manner of the present invention, when the distance between first pass tubes is 2.8 times of outer diameter thereof, and the distance between second pass tubes is 4.1 times of outer diameter thereof, 54 groups of radiant tubes (type 2-1) can be arranged in the same furnace chamber, this increases the productivity by 12.5%, at this time due to the distance between adjacent radiant tubes is increased, more uniform radiant conduction is obtained, this case is apparently advantageous for revamping old furnaces, and can remarkably increase productivity under condition of minimum investment.

[0052] During high temperature cracking by means of said apparatus, controlling the top/bottom burners heat supply ratio R=3:7, the hydrocarbons feedstock and dilution steam mixture passes through multi-path convection tubes 1, horizontally extended in convection section 2, after recovering the heat of fuel gas in convection section and preheating to the temperature of crossover section, the hydro carbons feedstock passes through the convection tubes 1 into cross tube 5, after distributing an appropriate current by distributor, into radiant tubes 7, vertically arranged in radiant section 3, the cracked product is heat exchanged in transfer line exchanger 4. The pyrolysis furnace is fully based on the heat supplied by bottom burners 8 and top burners 9, and at same time the fuel gas, produced from top and bottom burners passes through the horizontally arranged crossover section 6, providing convection heat to convection section 2.

EXAMPLE 2

[0053] A pyrolysis furnace has the yield of ethylene of 60 kilo-ton per year, said pyrolysis furnace comprising: a radiant section with furnace chamber height of about 14 m; a convection section, shifted from radiant section, with height about 14 m; a crossover section, horizontally arranged and extended between said radiant section and convection section; the upper edge of outlet of cross over section is located about 3 m from top portion of furnace chamber; 24 top burners arranged symmetrically about the center line of top portion, and 24 bottom burners, arranged symmetrically about the center line of bottom portion; multiple groups of convection tubes, horizontally arranged in convection section, and 32 groups of radiant tubes (type 2-1), vertically arranged in radiant section.

[0054] Because the location of cross over section is shift down about 3 m, the overall length of furnace is cut down about 3 m, where as the pyrolysis furnace of the same scale, employing wall and bottom burners combined heat supply manner, need to comprise 24 bottom burners and 72 wall burners.

[0055] The radiant tubes are arranged by former single row arrangement, the length of furnace chamber is about 15 m, the radiant tubes are two pass non-branched tubes (type 1-1), In order to avoid the mutual overlap radiant tubes bends and connected tubes in lower portion of furnace chamber, the distance between first pass tubes is 2.8 times of outer diameter thereof, and the distance between second pass tubes is 2.3 times of outer diameter thereof, in addition, it is a single row arrangement, only 48 groups radiant tubes can be arranged. In reconstruction design, the radiant tubes employ the arrangement manner of the present invention, all the first pass tubes are located at one plane, and all the second pass tubes are located at another plane, the distance between two planes is 350 mm, when the distance between first pass tubes is 2.8 times of outer diameter thereof, and the distance between second pass tubes is 2.3 times of outer diameter thereof, the radiant tubes employ the arrangement manner of the present invention, 108 groups two pass non-branched tubes with different diameters (type 1-1) can be arranged, this increases productivity to about 220%, at same time, various radiant tubes have uniform heat conduction, in addition, the form and weight of bends in various groups and manifold are fully the same, these components have high versatility, and all bends and connected tubes are parallel arranged in lower portion of furnace chamber, without interference, and are simple for manufacture and maintenance.

[0056] During high temperature cracking by means of said apparatus, controlling top/bottom burners heat supply ratio R=4:6, the hydrocarbons feed stock and dilution steam mixture passes through the multi-path convection tubes 1, horizontally extended in convection section 2, after recovering the heat of fuel gas in convection section, the hydro carbons feedstock passes through convection tubes 1 into cross tube 5, after distributing an appropriate current by distributor, passes into radiant tubes 7, vertically arranged in radiant section 3. The pyrolysis furnace is fully based on the heat, supplied by bottom burners 8 and top burners 9, and at the same time, the fuel gas, produced from top and bottom burners passes through the horizontally arranged crossover section 6, providing convection heat to the convection section 2.

EXAMPLE 3

[0057] a pyrolysis furnace has the same pyrolysis furnace of example 1, but employing radiant tubes type 4-1. If single row of radiation tubes is employed, the distance between first pass tubes is about 1.8 times of the outer diameter thereof, the distance between second pass tubes is about 1.4 times of the outer diameter thereof, in this case 32 groups of radiant tubes can be arranged, instead, employing the arrangement manner of radiant tubes of the present invention, the distance between first pass tubes still maintain 1.8 times of the outer diameter thereof, but the distance between second pass tubes is increased to 3.8 times of the outer diameter there of, all the first pass tubes are located at one plane, all the second pass tubes are located at another plane, the distance between two planes is 350 mm, This increases the productivity by about 50%. If the distance between first pass tubes enlarged to 2.4 times of the outer diameter thereof, the distance between second pass tubes enlarged to 5.1 times of outer diameter there of, and the distance between first and second pass tubes is 350 mm, in this case, 36 groups of radiant tubes can be arranged, this increases the productivity by about 12%, at this time, due to the enlargement of distance between tubes, the ability for radiant convection by radiant tubes is far better than radiant tubes-employing single row arrangement.

Claims

1. A pyrolysis furnace with new type radiant tubes arrangement, comprising:

a) vertically arranged radiant section (3), in which burners and multiple groups of radiant tubes (7) are arranged for high temperature cracking hydrocarbons feedstock;

b) vertically arranged convection section (2), located above the radiant section and axially shifted therewith, in said convection section multiple groups of convection tubes (1) are arranged for preheating the hydrocarbons feedstock;

c) horizontally arranged crossover section (6), connected between said radiant section (3) and said convection section (2);

characterized in that,

said multiple groups radiant tubes (7) are two pass tubes with different diameters, the first pass tubes and second pass tubes in various groups are located at two parallel planes, and the projection of each second pass tube is corresponding to the center location of the projection connecting line, of the two first pass tubes adjacent therewith, the structure of each first pass tube and second pass tube is the same.

2. The pyrolysis furnace according to claim 1, wherein said radiant tubes (7) are type 2-1 of two pass branched tubes with different diameters.

3. The pyrolysis furnace according to claim 1, wherein said radiant tubes (7) are type 4-1 of two pass branched tubes with different diameters.

4. The pyrolysis furnace according to claim 1, wherein said radiant tubes. (7) are type 1-1 of two pass non-branched tubes with different diameters.

5. The pyrolysis furnace according to claims 1-4, wherein the distance between two adjacent radiant tubes (7) is 1.8-6.0 times of outer diameter of radiant tubes at the same plane.

6. The pyrolysis furnace according to claims 1-4, wherein the distance between two adjacent radiant tubes (7) is 1.8˜4.2 times of outer diameter of radiant tubes at the same plane.

7. The pyrolysis furnace according to claims 1-4, wherein the distance between two adjacent radiant tubes (7) is 2.0˜2.8 times of outer diameter of radiant tubes at the same plane.

8. The pyrolysis furnace according to claims 1-4, wherein the distance between the planes where said first pass tubes and second pass tubes in every group of radiant tubes (7) are respectively located is 100-600 mm.

9. The pyrolysis furnace according to claims 1-4, wherein the distance between the planes where said first pass tubes and second pass tubes in every group of radiant tubes (7) are respectively located is 200-500 mm.

10. The pyrolysis furnace according to claims 1-4, wherein the distance between the planes where said first pass tubes and second pass tubes in every group of radiant tubes (7) are respectively located is 300-400 mm.

11. The pyrolysis furnace according to claim 1, wherein bottom burners (8) and top burners (9) are simultaneously arranged in said radiant section (3), more over, said crossover section (6) is extended out from a middle-upper portion of sidewall of radiant section (3) and connected to bottom portion of convection section (2).

12. The pyrolysis furnace according to claim 11, wherein the top wall of said cross over section (6) is located under the top wall of said radiant section (3), its distance H is determined by the top/bottom burners (9,8) heat supply ratio R, when R varies in a range of 1:9˜7:3, H is 10%˜50% of total height of radiant section (3).

13. The pyrolysis furnace according to claim 11, wherein when R varies in a range of 2:8˜6:4, H is 10%˜40% of total height of radiant section (3).

14. The pyrolysis furnace according to claim 11, wherein when R varies in a range of 2.5:7.5-5:5, H is 15%-40% of total height of radiant section (3).

15. The pyrolysis furnace according to claim 11, wherein when R varies in a range of 3:7˜4:6, H is 20%˜40% of total height of radiant section (3).

16. The pyrolysis furnace according to claim 11, wherein the number of said bottom burners (8) is equal to the number of said top burners (9), the top or bottom burners are arranged symmetrically about centerline of top or bottom portions and corresponding to one another at top or bottom portion respectively.

17. A method of high temperature cracking hydrocarbons feedstock by means of a pyrolysis furnace according to any one of claims 1-16, comprising:

at convection section (2), preheating the hydrocarbons feedstock in radiant tubes (1), utilizing fuel gas of crossover section, came from radiant section (3); at radiant section (3), high temperature cracking the preheated hydrocarbons feedstock in radiant tubes (7), utilizing the heat supplied by top burners (9) and bottom burners (8); wherein maintaining the heat supplied by bottom burners (8) constant, by means of regulating the heat supplied by top burners (9) so as to satisfy the temperature requirement for cracking different hydrocarbons feedstock.

18. The use of pyrolysis furnace according to any one of claims 1-16 for high temperature cracking Hydrocarbons.