CA1303071C - Method of thermally decomposing hydrocarbon and thermal decomposition tube - Google Patents
Method of thermally decomposing hydrocarbon and thermal decomposition tubeInfo
- Publication number
- CA1303071C CA1303071C CA000563686A CA563686A CA1303071C CA 1303071 C CA1303071 C CA 1303071C CA 000563686 A CA000563686 A CA 000563686A CA 563686 A CA563686 A CA 563686A CA 1303071 C CA1303071 C CA 1303071C
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- Canada
- Prior art keywords
- thermal decomposition
- tube
- hydrocarbons
- fin
- fins
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0053—Details of the reactor
- B01J19/006—Baffles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0006—Controlling or regulating processes
- B01J19/002—Avoiding undesirable reactions or side-effects, e.g. avoiding explosions, or improving the yield by suppressing side-reactions
- B01J19/0026—Avoiding carbon deposits
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/02—Apparatus characterised by being constructed of material selected for its chemically-resistant properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/24—Stationary reactors without moving elements inside
- B01J19/2415—Tubular reactors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/24—Stationary reactors without moving elements inside
- B01J19/2415—Tubular reactors
- B01J19/2425—Tubular reactors in parallel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/00761—Details of the reactor
- B01J2219/00763—Baffles
- B01J2219/00765—Baffles attached to the reactor wall
- B01J2219/0077—Baffles attached to the reactor wall inclined
- B01J2219/00772—Baffles attached to the reactor wall inclined in a helix
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/02—Apparatus characterised by their chemically-resistant properties
- B01J2219/025—Apparatus characterised by their chemically-resistant properties characterised by the construction materials of the reactor vessel proper
- B01J2219/0277—Metal based
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention is concerned with a method of thermally decomposing hydrocarbons and a thermal decomposition tube used therefor. A plurality of spiral fins are formed on the inner wall of the thermal decomposition tube. Since no-fin portions are formed on portions where the fins are cut away, the flow of hydrocarbons through the no-fin portions is turbulent to a suitable degree. For this reason, coke is prevented from adhering to the inner wall of the thermal decomposition tube.
The present invention is concerned with a method of thermally decomposing hydrocarbons and a thermal decomposition tube used therefor. A plurality of spiral fins are formed on the inner wall of the thermal decomposition tube. Since no-fin portions are formed on portions where the fins are cut away, the flow of hydrocarbons through the no-fin portions is turbulent to a suitable degree. For this reason, coke is prevented from adhering to the inner wall of the thermal decomposition tube.
Description
METHOD OF THERMALLY DECOMPOSING HYDROCARBON
AND THERMAL DECOMPOSITION TUBE
BACKGRO~ND OF THE INVENTION
1. Field of the Invention This invention relates to improvements in a method of thermally decomposing hydrocarbons, wherein useful olefins such as ethylene and propylene are manufactured by thermal decomposition of hydrocarbons and in the thermal decomposition tube itself.
AND THERMAL DECOMPOSITION TUBE
BACKGRO~ND OF THE INVENTION
1. Field of the Invention This invention relates to improvements in a method of thermally decomposing hydrocarbons, wherein useful olefins such as ethylene and propylene are manufactured by thermal decomposition of hydrocarbons and in the thermal decomposition tube itself.
2. Description of the Related Art In general, for manufacturing olefins, particularly ethylene, by thermal decomposition of hydrocarbons, there has been adopted a method wherein a thermal decomposition furnace incorporating thermal decomposition tubes is used, hydrocarbons are heated to a predetermined termperature for thermal decomposition, and thereafter, quenched. In this case, in order to increase the heat transfer rate to a fluid in the thermal decomposition tubes, various devices have been used wherein fins or raised portions are provided on the inner or outer surfaces of the thermal decomposition tubes, and the tubes are formed so as to have elliptical sectional configurations. In order to improve the yield of olefin, and particularly, the yield of useful ethylene, such devices have been used wherein the residence time in the ~303071 thermal composition tubes is shortened, and cooled as quickly as possible and so on.
However, if the reaction conditions are made severe in order to improve the degree of conversion, then adhesion of by-product coke to the interior of the thermal decomposition tubes is notable. Then there is the necessity of frequently removing the adhering coke. Heretofore, anyway, the efficiency of the method of thermal decomposition as a whole has not been improved.
It is already known that, in order to raise the heat transfer rate in the thermal decomposition tube, a metal tube having on the inner surface thereof spiral fins is used as the thermal decomposition tube in an apparatus for thermally decomposing hydrocarbons (Japanese Paten~ Kokai (Laid-Open) Nos.
58-132081 and 58-173022).
However, since the thermal decomposition tube for hydrocarbons is used under particularly severe conditions, adhesion of by-product coke is heavy, thus presenting such disadvantages that, in order to secure a given operating efficiency, coke must be frequently removed, which is found to be too troublesome.
To manufacture one or more metal tubes having a predetermi.ned length in one structure is technically difficult from the viewpoint of the manufacturing technology so that a number of metal tubes should necessarily be connected to each other by welding. However, it is difficult to butt-weld these 130;~071 metal tubes with the end faces of the fins perfectly coinciding with each other, thus causing a problem that the coke adheres to the portions where the fins do not perfectly coincide with each other, thereby lowering the operating efficiency.
However, heretofore, the shape and other characteristics of the thermal decomposition tubes have not been studied in detail SUMMARY OF THE INVENTION
One object of the present invention is to provide a method of thermally decomposing hydrocarbons wherein depositon of coke in the thermal decomposition tubes is low, to thereby improve the operating efficiency of the apparatus as a whole, and of the thermal decomposition tubes thereof.
In the method according to the present invention, wherein a metal tube having fins on the inner wall surface thereof is used as a thermal decomposition tube, and hydrocarbons are made to flow through the metal tube for thermal decomposition, portions of the fins are cut away at a predetermined angle to form no-fin portions and the hydrocarbons are made to flow through the thermal decomposition tube.
To this end, in short, the present invention, being based on the fact that, in the thermal decomposition tube having fins on the inner surface thereof, coke notably adheres onto the inner wall surface, provides no-fin portions on the inner wall surface ,~. a , . ,~ ~, ~.
~3()307~
of the thermal decomposition tubes, whereby flow of the fluid is turbulent to a suitable degree, so that coke can be prevented from adhering to the inner wall surface.
The hydrocarbons useful in the method according to the present invention are from naphtha to heavy gas oil, and further, gaseous aliphatic hydrocarbons whereby useful olefins such as ethylene can be manufactured.
The thermal decomposition tubes according to the present invention are constructed so that, particularly, at portions where the metal tubes are connected to each other, portions of the fins are cut away at a predetermined angle to form portions without fins, whereby the necessity of butt-welding between the fin end faces, when the metal tubes are connected to each other, can be eliminated, and the problem of adhesion of coke, which appears at connected portions between the metal tubes where the end faces of fins cannot be perfectly coincidentally connected to each other, can be solved by making the flow of the fluid turbulent to a suitable degree, so that the efficiency of thermal decomposition of hydrocarbons can be improved.
The thermal decomposition furnace used according to the present invention may be any type of ordinary thermal decomposition furnace, but a multiple tube type thermal decomposition furnace is preferable because it has no curved tube portions.
130307~
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram of the arrangement of a thermal decomposition apparatus embodying the present invention;
Fig. 2 is a partial sectional view showing the essential features of a metal tube used in a thermal decomposition apparatus of the present invention;
Fig. 3 is a flattened view of the metal tube; and Fig. 4 is a sectional view taken along the line III - III
in Fig. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
One embodiment of the present invention will be described with reference to the accompanying drawings.
Fig. 1 shows a schematic diagram of an arrangement of the thermal decomposition apparatus. Referring to this drawing, thermal decomposition furnace 1 has burners 2 and twelve straight thermal decomposition tubes 3. The inlets of thermal decomposition tubes 3 are connected to inlet headers 4, the outlets thereof are connected to outlet headers 5, the inlet headers 4 being connected to material feed line 6, and outlet headers 5 being connected to quenching devices 7, respectiveiy, outside the furnace.
Material feed line 6 supplies hydrocarbon and steam, these materials being preheated by preheaters 8 and 9, respectively, and which are then fed to inlet headers 4.
r~
130307~
Thermal decomposition tube 3 is one in which portions of the fins are cut away at a predetermined angle to form no-fin portions 15 (Fig. 2). The flow of hydrocarbons is made turbulent by these no-fin portions 15, thus resulting in decreased adhesion of coke and improved efficiency of thermal decomposition of hydrocarbons. Incidentally, the turbulence referred to herein is relative to the regulated flow of hydrocarbons by spiral fins.
Various methods of manufacturing the thermal decomposition tube or tubes may be used as for example by fusion, cold drawing or the like. A metal tube of suitable length may be manufactured by these methods. According to the present invention, it is desirable to use a metal tube wherein predetermined no-fin portions are provided at a plurality of positions spaced 3 - lOm apart from each other, and particularly at positions where metal tubes are connected to each other. Fig.
2 shows an example in which two metal tubes 11 are welded to each other in the axial directions thereof to form the metal tube of suitable length. These metal tubes 11 are formed of a nickel-chromium alloy for example, and each is integrally provided on the inner peripheral surface thereof with a plurality of fins 13 each having a semi-circular arcuate configuration. As shown in Fig. 4, eight rows of fins 13 are formed at regular intervals in the circumferential direction of metal tube 11, each having a wave-shaped sectional configuration, and as shown in Fig. 3, are formed into a helical shape, extending out at an angle of ~ 6-. ~ ' ~30307i inclination ~2 inclined to a line perpendicularly intersecting the longitudinal direction of the metal tube 11.
It is preferable that the angle of inclination ~2 is 5 -20, and particularly, 7 - 15. This is because, if the angle of inclination is 5 or less, then, provision of helical grooves is not satisfactory as to the effect thereof, while, if the angle of inclination exceeds 20, then, pressure loss in the tube-is undesirably increased. Fin 13 is formed such that, as indicated in the aforesaid Patent Kokai (Laid-Open) No. 58-173022 for example, when the meal tube 11 is hot-extruded, straight fins are formed on the inner surface of metal tube 11, and therafter, metal tube 11 is subjected to twisting in the circumferential direction thereof.
The end portions to be abutted against each other of the metal tubes 11 are formed to provide bevelled portions llA where the outer diameter of the metal tube 11 is reduced by two steps, whereby the surfaces to be abutted against each other of the metal tube 11 are welded together wholly, so that a firm connection can be achieved. In this case, the aforesaid bevelled portion llA may be formed at least at an end portion of either one of the metal tubes. An end portion of fin 13 is cut away at an angle ~1 from a position slightly inward of the end edge of the metal tube 11, the end edge is formed into a slanted portion 13A coinciding with the inner diametrical surface of the metal tube 11, and a predetermined length L from the end edge of the slanted portion ~ -7-~, ~
i303071 13A to the end edge of the metal tube 11 is no-fin portion 15. In this case, the angle of cut away d~1 is determined to be 75 or less, and preferably is within a range of 8 - 30, in particular from the viewpoint of obtaining proper flow of the fluid. If the angle of cut-away ~1 is higher than 75, then the flow of the fluid is more turbulent than necessary, and adhesion of coke is accelerated, thus undesirably causing corrosion of the tube. It is preferable that the length L of the no-fin portion 15 is a length obtained in accordance with the formula:
(t2/t1) x 10 < L < (t2/t1) x 200 where t1 represents the wall thickness of the metal tube 11 where no fin is formed, and t2 represents the height of fin 13. In this case, if the length L of no-fin portion 15 is less than (t2/tl) x 10, then the effect on prevention of coke adherence is low and welding between the metal tubes 11 is difficult. If length L is greater than (t2/tl) x 200, then when hydrocarbons and the like at high temperature flow through the metal tubes 11 after welding, the turbulence of the flow is excessively high and the welded portions become partially heated to a high temperature, whereby so-called hot spots occur.
Incidentally, as a prferred example of the metal tube 11, there may be exemplified one having an outer diameter = 40 - 60mm, a diameter of the base of the fin d1 = 25 - 45mm, a diameter of 130307~
the crest of the fin d2 = 13 - 35mm, a wall thickness tl = 3 -lOmm, a height of fin t2 = 3 - lOmm, a number of the fins = 5 -10, a fin pitch = 300 - 500mm, a length of cut-away portion L =
100 - 350mm, an angle of cut away ~1 = 8 - 30, an an interval between the cut-away portions = 4 - 8m.
In welding the metal tubes 11 to each other, as shown in Fig. 2, bevelled portions llA are formed at the end portions of two metal tubes 11 and the bevelled portions llA are abutted against each other in such a way so that fins 13 are aligned on one and the same extension as shown in Fig. 3. In this case, the end edge of the fin 13 in the metal tube 11 is positioned inwardly of the end edge of the metal tube 11 by a length L/2 of no-fin portion 15 through the slanted portion 13A, so that abutment of the metal tubes against each other can be sufficiently made only if the bevelled portions llA are abutted against each other.
Subsequently, the bevelled portions llA are welded to each other by arc welding, gas welding or the like, whereby connection between the metal tubes 11 is completed.
This embodiment can offer the following advantages.
More specificially, metal tubes 11 are formed with no-fin portion 15 and used as the thermal decomposition tube, so that coke is prevented from adhering to the welded portions to the utmost, the necessity of frequently removing coke is eliminated, and the operating efficiency of the thermal decomposition apparatus as a whole is improved.
~30307~
The end portion of fin 13 is formed to provide slanted portion 13A having a predetermined angle of cut-away ~1/ so that the fluid in metal tubes ll can flow smoothly, and adhesion of coke to slanted portions 13A can be avoided.
Moreover, in butt-welding metal tubes 11 to each other, the necessity of strict positioning work as in conventional welding is eliminated, so that the thermal decomposition tube can be manufactured in a simplified manner.
The present invention will be specifically described in conjunction with an example of the following experiment using the thermal decomposition apparatus for hydrocarbons as described below.
Thermal decomposition tube 3 used in the above thermal d~composition apparatus was formed of a nickel-chromium alloy and had an outer diameter Do = 49.7mm, a diameter of the base of the fin dl = 36.2mm, a diameter of the crest of the fin d2 = 24.2mm, wall thickness tl = 6.Omm, height of the fin t2 = 6.Omm, number of the fins = 8, fin pitch = 40Omm and length of the thermal decomposition tube ~ = llm. As the hydrocarbon material, naphtha was used, and the thermal decomposiiton was performed under the conditions of steam/hydrocarbon weight ratio = 0.5, inlet temperature of thermal decomposition tube 3 = 600C, inlet pressure = 2.0kg/cm2G, outlet temperature of the thermal decomposition tube = 880C, outlet pressure = l.Okg/cm2G, residence time 100 milliseconds, to thereby obtain a product having ethylene as the main component.
~303071 Thermal decomposition tube 3 was constructed so that two metal tubes 11 each having a length of 5.Sm were welded to each other. As the conditions of welding, four groups were adopted.
Group 1 had the conditions in welding of length of cut-away portion L = 30mm and angle of cut-away ~1 = 15, Group 2 had the conditions of L = 220mm and ~1 = 15, Group 3 had the conditions of L = 30mm and ~ 1 = 80, and Group 4 had the conditions of having no cut-away portions. Here, Group 1 was under the conditions of the present invention.
The following Table shows the results.
TABLE
\ TEMPEKATURE IMMED- TE~PERATURE AETER
\ IATELY AFTER START 20 DAYS'OPERATION
\ OE OPERAT ION
\ POSITION A POSITlON B POSITION A ~POSITION B
. GROUP I lOOO'C lOOO-C 1040'C 1040'C
~GROUP 2 1000 C 1015'C 1040'C 1070 C
GROUP 3 1000 C 1000'C lOSO'C 1040'C
GROUP 4 1000'C IOOO'C 1060'C 1040 C
POSITION A: SOOmm downstream from the abutment between the metal tubes POSITION B: 1Omm downstream from the abutment between the metal tubes ~.
130307~
As apparent from the above experiments, if the welding method of Group 2 is adopted, it is known that the welded portion becomes a hot spot, whereby the coking rate if high. Groups 3 and 4 are not problematical as to temperature. However, since Group 3 has a large angle of cut-away ~1~ and Group 4 has no cut-away portions, the flow downstream of the welded portion is turbulent to a considerable extent, whereby coking is accelerated, thus presenting a problem in practice.
In practice, the section of the fin need not necessarily be a convex shape, and may be a square shape or the like. The material of metal tube 11 need not necessarily be a nickel-chromium alloy, and may be formed of any of other metallic material.
Thermal decomposition tube 3 has been constructed so that the two metal tubes 11 are welded to each other; however, the number of metal tubes is to be determined in accordance with the length thereof, and the respective welded portions are each formed with no-fin portion 15.
The present invention with the above-described arrangement is advantageous in providing a method of thermal decomposition of hydrocarbons, wherein deposition of coke in the thermal decomposition tube is low, so that the operating efficiency of the thermal decomposition apparatus as a whole is improved.
:. -12-, -'- ';
However, if the reaction conditions are made severe in order to improve the degree of conversion, then adhesion of by-product coke to the interior of the thermal decomposition tubes is notable. Then there is the necessity of frequently removing the adhering coke. Heretofore, anyway, the efficiency of the method of thermal decomposition as a whole has not been improved.
It is already known that, in order to raise the heat transfer rate in the thermal decomposition tube, a metal tube having on the inner surface thereof spiral fins is used as the thermal decomposition tube in an apparatus for thermally decomposing hydrocarbons (Japanese Paten~ Kokai (Laid-Open) Nos.
58-132081 and 58-173022).
However, since the thermal decomposition tube for hydrocarbons is used under particularly severe conditions, adhesion of by-product coke is heavy, thus presenting such disadvantages that, in order to secure a given operating efficiency, coke must be frequently removed, which is found to be too troublesome.
To manufacture one or more metal tubes having a predetermi.ned length in one structure is technically difficult from the viewpoint of the manufacturing technology so that a number of metal tubes should necessarily be connected to each other by welding. However, it is difficult to butt-weld these 130;~071 metal tubes with the end faces of the fins perfectly coinciding with each other, thus causing a problem that the coke adheres to the portions where the fins do not perfectly coincide with each other, thereby lowering the operating efficiency.
However, heretofore, the shape and other characteristics of the thermal decomposition tubes have not been studied in detail SUMMARY OF THE INVENTION
One object of the present invention is to provide a method of thermally decomposing hydrocarbons wherein depositon of coke in the thermal decomposition tubes is low, to thereby improve the operating efficiency of the apparatus as a whole, and of the thermal decomposition tubes thereof.
In the method according to the present invention, wherein a metal tube having fins on the inner wall surface thereof is used as a thermal decomposition tube, and hydrocarbons are made to flow through the metal tube for thermal decomposition, portions of the fins are cut away at a predetermined angle to form no-fin portions and the hydrocarbons are made to flow through the thermal decomposition tube.
To this end, in short, the present invention, being based on the fact that, in the thermal decomposition tube having fins on the inner surface thereof, coke notably adheres onto the inner wall surface, provides no-fin portions on the inner wall surface ,~. a , . ,~ ~, ~.
~3()307~
of the thermal decomposition tubes, whereby flow of the fluid is turbulent to a suitable degree, so that coke can be prevented from adhering to the inner wall surface.
The hydrocarbons useful in the method according to the present invention are from naphtha to heavy gas oil, and further, gaseous aliphatic hydrocarbons whereby useful olefins such as ethylene can be manufactured.
The thermal decomposition tubes according to the present invention are constructed so that, particularly, at portions where the metal tubes are connected to each other, portions of the fins are cut away at a predetermined angle to form portions without fins, whereby the necessity of butt-welding between the fin end faces, when the metal tubes are connected to each other, can be eliminated, and the problem of adhesion of coke, which appears at connected portions between the metal tubes where the end faces of fins cannot be perfectly coincidentally connected to each other, can be solved by making the flow of the fluid turbulent to a suitable degree, so that the efficiency of thermal decomposition of hydrocarbons can be improved.
The thermal decomposition furnace used according to the present invention may be any type of ordinary thermal decomposition furnace, but a multiple tube type thermal decomposition furnace is preferable because it has no curved tube portions.
130307~
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram of the arrangement of a thermal decomposition apparatus embodying the present invention;
Fig. 2 is a partial sectional view showing the essential features of a metal tube used in a thermal decomposition apparatus of the present invention;
Fig. 3 is a flattened view of the metal tube; and Fig. 4 is a sectional view taken along the line III - III
in Fig. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
One embodiment of the present invention will be described with reference to the accompanying drawings.
Fig. 1 shows a schematic diagram of an arrangement of the thermal decomposition apparatus. Referring to this drawing, thermal decomposition furnace 1 has burners 2 and twelve straight thermal decomposition tubes 3. The inlets of thermal decomposition tubes 3 are connected to inlet headers 4, the outlets thereof are connected to outlet headers 5, the inlet headers 4 being connected to material feed line 6, and outlet headers 5 being connected to quenching devices 7, respectiveiy, outside the furnace.
Material feed line 6 supplies hydrocarbon and steam, these materials being preheated by preheaters 8 and 9, respectively, and which are then fed to inlet headers 4.
r~
130307~
Thermal decomposition tube 3 is one in which portions of the fins are cut away at a predetermined angle to form no-fin portions 15 (Fig. 2). The flow of hydrocarbons is made turbulent by these no-fin portions 15, thus resulting in decreased adhesion of coke and improved efficiency of thermal decomposition of hydrocarbons. Incidentally, the turbulence referred to herein is relative to the regulated flow of hydrocarbons by spiral fins.
Various methods of manufacturing the thermal decomposition tube or tubes may be used as for example by fusion, cold drawing or the like. A metal tube of suitable length may be manufactured by these methods. According to the present invention, it is desirable to use a metal tube wherein predetermined no-fin portions are provided at a plurality of positions spaced 3 - lOm apart from each other, and particularly at positions where metal tubes are connected to each other. Fig.
2 shows an example in which two metal tubes 11 are welded to each other in the axial directions thereof to form the metal tube of suitable length. These metal tubes 11 are formed of a nickel-chromium alloy for example, and each is integrally provided on the inner peripheral surface thereof with a plurality of fins 13 each having a semi-circular arcuate configuration. As shown in Fig. 4, eight rows of fins 13 are formed at regular intervals in the circumferential direction of metal tube 11, each having a wave-shaped sectional configuration, and as shown in Fig. 3, are formed into a helical shape, extending out at an angle of ~ 6-. ~ ' ~30307i inclination ~2 inclined to a line perpendicularly intersecting the longitudinal direction of the metal tube 11.
It is preferable that the angle of inclination ~2 is 5 -20, and particularly, 7 - 15. This is because, if the angle of inclination is 5 or less, then, provision of helical grooves is not satisfactory as to the effect thereof, while, if the angle of inclination exceeds 20, then, pressure loss in the tube-is undesirably increased. Fin 13 is formed such that, as indicated in the aforesaid Patent Kokai (Laid-Open) No. 58-173022 for example, when the meal tube 11 is hot-extruded, straight fins are formed on the inner surface of metal tube 11, and therafter, metal tube 11 is subjected to twisting in the circumferential direction thereof.
The end portions to be abutted against each other of the metal tubes 11 are formed to provide bevelled portions llA where the outer diameter of the metal tube 11 is reduced by two steps, whereby the surfaces to be abutted against each other of the metal tube 11 are welded together wholly, so that a firm connection can be achieved. In this case, the aforesaid bevelled portion llA may be formed at least at an end portion of either one of the metal tubes. An end portion of fin 13 is cut away at an angle ~1 from a position slightly inward of the end edge of the metal tube 11, the end edge is formed into a slanted portion 13A coinciding with the inner diametrical surface of the metal tube 11, and a predetermined length L from the end edge of the slanted portion ~ -7-~, ~
i303071 13A to the end edge of the metal tube 11 is no-fin portion 15. In this case, the angle of cut away d~1 is determined to be 75 or less, and preferably is within a range of 8 - 30, in particular from the viewpoint of obtaining proper flow of the fluid. If the angle of cut-away ~1 is higher than 75, then the flow of the fluid is more turbulent than necessary, and adhesion of coke is accelerated, thus undesirably causing corrosion of the tube. It is preferable that the length L of the no-fin portion 15 is a length obtained in accordance with the formula:
(t2/t1) x 10 < L < (t2/t1) x 200 where t1 represents the wall thickness of the metal tube 11 where no fin is formed, and t2 represents the height of fin 13. In this case, if the length L of no-fin portion 15 is less than (t2/tl) x 10, then the effect on prevention of coke adherence is low and welding between the metal tubes 11 is difficult. If length L is greater than (t2/tl) x 200, then when hydrocarbons and the like at high temperature flow through the metal tubes 11 after welding, the turbulence of the flow is excessively high and the welded portions become partially heated to a high temperature, whereby so-called hot spots occur.
Incidentally, as a prferred example of the metal tube 11, there may be exemplified one having an outer diameter = 40 - 60mm, a diameter of the base of the fin d1 = 25 - 45mm, a diameter of 130307~
the crest of the fin d2 = 13 - 35mm, a wall thickness tl = 3 -lOmm, a height of fin t2 = 3 - lOmm, a number of the fins = 5 -10, a fin pitch = 300 - 500mm, a length of cut-away portion L =
100 - 350mm, an angle of cut away ~1 = 8 - 30, an an interval between the cut-away portions = 4 - 8m.
In welding the metal tubes 11 to each other, as shown in Fig. 2, bevelled portions llA are formed at the end portions of two metal tubes 11 and the bevelled portions llA are abutted against each other in such a way so that fins 13 are aligned on one and the same extension as shown in Fig. 3. In this case, the end edge of the fin 13 in the metal tube 11 is positioned inwardly of the end edge of the metal tube 11 by a length L/2 of no-fin portion 15 through the slanted portion 13A, so that abutment of the metal tubes against each other can be sufficiently made only if the bevelled portions llA are abutted against each other.
Subsequently, the bevelled portions llA are welded to each other by arc welding, gas welding or the like, whereby connection between the metal tubes 11 is completed.
This embodiment can offer the following advantages.
More specificially, metal tubes 11 are formed with no-fin portion 15 and used as the thermal decomposition tube, so that coke is prevented from adhering to the welded portions to the utmost, the necessity of frequently removing coke is eliminated, and the operating efficiency of the thermal decomposition apparatus as a whole is improved.
~30307~
The end portion of fin 13 is formed to provide slanted portion 13A having a predetermined angle of cut-away ~1/ so that the fluid in metal tubes ll can flow smoothly, and adhesion of coke to slanted portions 13A can be avoided.
Moreover, in butt-welding metal tubes 11 to each other, the necessity of strict positioning work as in conventional welding is eliminated, so that the thermal decomposition tube can be manufactured in a simplified manner.
The present invention will be specifically described in conjunction with an example of the following experiment using the thermal decomposition apparatus for hydrocarbons as described below.
Thermal decomposition tube 3 used in the above thermal d~composition apparatus was formed of a nickel-chromium alloy and had an outer diameter Do = 49.7mm, a diameter of the base of the fin dl = 36.2mm, a diameter of the crest of the fin d2 = 24.2mm, wall thickness tl = 6.Omm, height of the fin t2 = 6.Omm, number of the fins = 8, fin pitch = 40Omm and length of the thermal decomposition tube ~ = llm. As the hydrocarbon material, naphtha was used, and the thermal decomposiiton was performed under the conditions of steam/hydrocarbon weight ratio = 0.5, inlet temperature of thermal decomposition tube 3 = 600C, inlet pressure = 2.0kg/cm2G, outlet temperature of the thermal decomposition tube = 880C, outlet pressure = l.Okg/cm2G, residence time 100 milliseconds, to thereby obtain a product having ethylene as the main component.
~303071 Thermal decomposition tube 3 was constructed so that two metal tubes 11 each having a length of 5.Sm were welded to each other. As the conditions of welding, four groups were adopted.
Group 1 had the conditions in welding of length of cut-away portion L = 30mm and angle of cut-away ~1 = 15, Group 2 had the conditions of L = 220mm and ~1 = 15, Group 3 had the conditions of L = 30mm and ~ 1 = 80, and Group 4 had the conditions of having no cut-away portions. Here, Group 1 was under the conditions of the present invention.
The following Table shows the results.
TABLE
\ TEMPEKATURE IMMED- TE~PERATURE AETER
\ IATELY AFTER START 20 DAYS'OPERATION
\ OE OPERAT ION
\ POSITION A POSITlON B POSITION A ~POSITION B
. GROUP I lOOO'C lOOO-C 1040'C 1040'C
~GROUP 2 1000 C 1015'C 1040'C 1070 C
GROUP 3 1000 C 1000'C lOSO'C 1040'C
GROUP 4 1000'C IOOO'C 1060'C 1040 C
POSITION A: SOOmm downstream from the abutment between the metal tubes POSITION B: 1Omm downstream from the abutment between the metal tubes ~.
130307~
As apparent from the above experiments, if the welding method of Group 2 is adopted, it is known that the welded portion becomes a hot spot, whereby the coking rate if high. Groups 3 and 4 are not problematical as to temperature. However, since Group 3 has a large angle of cut-away ~1~ and Group 4 has no cut-away portions, the flow downstream of the welded portion is turbulent to a considerable extent, whereby coking is accelerated, thus presenting a problem in practice.
In practice, the section of the fin need not necessarily be a convex shape, and may be a square shape or the like. The material of metal tube 11 need not necessarily be a nickel-chromium alloy, and may be formed of any of other metallic material.
Thermal decomposition tube 3 has been constructed so that the two metal tubes 11 are welded to each other; however, the number of metal tubes is to be determined in accordance with the length thereof, and the respective welded portions are each formed with no-fin portion 15.
The present invention with the above-described arrangement is advantageous in providing a method of thermal decomposition of hydrocarbons, wherein deposition of coke in the thermal decomposition tube is low, so that the operating efficiency of the thermal decomposition apparatus as a whole is improved.
:. -12-, -'- ';
Claims (16)
1. In a method for thermal decomposition of hydrocarbons, wherein hydrocarbons flow through a thermal decomposition tube provided on the inner surface thereof with fins, and are thereafter processed in a predetermined manner, the improvement wherein the flow of hydrocarbons is partially turbulent caused by no-fin portions provided in said thermal decomposition tube.
2. In a method for thermal decomposition of hydrocarbons as set forth in claim 1, wherein, when the wall thickness of a portion of said tube without fins is t1 and the height of the fin is t2, the length L of the no-fin portion is determined to be:
(t2/t1) x 10 ? L ? (t2/t1) x 200
(t2/t1) x 10 ? L ? (t2/t1) x 200
3. In a method for thermal decomposition of hydrocarbons as set forth in claim 1, wherein an angle of cut-away .theta.1 of said fin, with the inner wall surface of said thermal decomposition tube is:
.theta.1 ? 75°
.theta.1 ? 75°
4. In a method of thermal decomposition of hydrocarbons, as set forth in claim 3, wherein the angle .theta.1 of said fin is:
8° ? .theta.1 ? 30°
8° ? .theta.1 ? 30°
5. In a method of thermal decomposition of hydrocarbons as set forth in claim 1, wherein said fins are formed into helical shapes.
6. In a method of thermal decomposition of hydrocarbons as set forth in claim 5, wherein, with reference to a direction perpendicularly intersecting the longitudinal direction of said thermal decomposition tube, an angle of inclination of the helix of said fin is 5° - 20°.
7. A tube for the thermal decomposition of hydrocarbons wherein hydrocarbons flow in said thermal decomposition tube formed by connecting a plurality of metal tubes to each other, each being provided on the inner surface thereof with a plurality of fins, the improvement wherein a portion of each of said fins is cut away at a predetermined angle to form a no-fin portion.
8. A tube for the thermal decomposition of hydrocarbons as set forth in claim 7, wherein said no-fin portion is formed where the metal tubes are connected to each other.
9. A tube for the thermal decomposition of hydrocarbons as set forth in claim 7, wherein, when the wall thickness of a portion of said tubes without fins is t1 and the height of the fin is t2, the length L of the no-fin portion is determined to be:
(t2/t1) x 10 ? L ? (t2/t1) x 200
(t2/t1) x 10 ? L ? (t2/t1) x 200
10. A tube for the thermal decomposition of hydrocarbons as set forth in claim 7, wherein an angle of cut-away .theta.1 of said fin, with reference to the inner wall surface of said thermal decomposition tube is:
.theta.1 ? 75°
.theta.1 ? 75°
11. A tube for the thermal decomposition of hydrocarbons as set forth in claim 10, wherein the angle .theta.1 of said fin is:
8° ? .theta.1 ? 30°
8° ? .theta.1 ? 30°
12. A tube for the thermal decomposition of hydrocarbons as set forth in claim 7, wherein said fins are formed into helical shapes.
13. A tube for the thermal decomposition of hydrocarbons as set forth in claim 7, wherein the wall thickness of an end portion of at least one of said metal tubes, where said metal tubes are connected to each other, is progressively decreased.
14. A tube for the thermal decomposition of hydrocarbons as set forth in claim 12, wherein said fins have sectional shapes of waves.
15. A tube for the thermal decomposition of hydrocarbons as set forth in claim 12, wherein the number of said fins is 5 to 10, said fins being provided along the circumferential direction of said thermal decomposition tube.
16. A tube for the thermal decomposition of hydrocarbons as set forth in claim 12, wherein with reference to a direction perpendicularly intersecting the longitudinal direction of said thermal decomposition tube, an angle of inclination of the helix of said fin is 5° to 20°.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61131301A JPH0696708B2 (en) | 1986-06-06 | 1986-06-06 | Hydrocarbon pyrolysis method |
| CA000563686A CA1303071C (en) | 1986-06-06 | 1988-04-08 | Method of thermally decomposing hydrocarbon and thermal decomposition tube |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61131301A JPH0696708B2 (en) | 1986-06-06 | 1986-06-06 | Hydrocarbon pyrolysis method |
| CA000563686A CA1303071C (en) | 1986-06-06 | 1988-04-08 | Method of thermally decomposing hydrocarbon and thermal decomposition tube |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1303071C true CA1303071C (en) | 1992-06-09 |
Family
ID=25671826
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000563686A Expired - Lifetime CA1303071C (en) | 1986-06-06 | 1988-04-08 | Method of thermally decomposing hydrocarbon and thermal decomposition tube |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH0696708B2 (en) |
| CA (1) | CA1303071C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004046277A1 (en) | 2002-11-15 | 2004-06-03 | Kubota Corporation | Cracking tube with spiral fin |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ITMI20040040A1 (en) * | 2004-01-15 | 2004-04-15 | Maurizio Spoto | INCREASED HEAT EXCHANGER ELEMENT |
| US9296666B2 (en) * | 2013-03-06 | 2016-03-29 | Exxonmobil Chemical Patents Inc. | Pyrolysis furnace tube joint |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58132081A (en) * | 1982-01-08 | 1983-08-06 | Idemitsu Petrochem Co Ltd | Thermal cracking of hydrocarbon |
-
1986
- 1986-06-06 JP JP61131301A patent/JPH0696708B2/en not_active Expired - Lifetime
-
1988
- 1988-04-08 CA CA000563686A patent/CA1303071C/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004046277A1 (en) | 2002-11-15 | 2004-06-03 | Kubota Corporation | Cracking tube with spiral fin |
| EP1561795A1 (en) * | 2002-11-15 | 2005-08-10 | Kubota Corporation | Cracking tube with spiral fin |
| EP1561795A4 (en) * | 2002-11-15 | 2011-08-17 | Kubota Kk | Cracking tube with spiral fin |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0696708B2 (en) | 1994-11-30 |
| JPS62288688A (en) | 1987-12-15 |
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