JPH09264683A - Pyrolysis reaction tube with fin for petrochemistry - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To prevent and prevent a local temperature rise due to stagnation and vortex of fluid near a fin in a pyrolysis reaction tube in which fins are formed on the inner surface of the tube in order to enhance heat transferability of the tube. , The function of the fin is effectively exerted. SOLUTION: The fin (2) of this pyrolysis reaction tube has the following shapes or materials (a) to (d). (A)
An inclined surface (3) that slopes down from the top of the fin is formed on the back side of the fin (downstream side in the fluid flow direction), (b)
The fins on the front side and the back side of the fin have inclined surfaces (4
Through holes (5 ₁ ) to (5 ₄ ) for allowing the fluid in the pipe to flow are formed in the fin (c) which is _1, 4 ₂ ).
(D) The fins are made of a material having better thermal conductivity than the base material pipe pair. As a result of the shape effect of the fins (2) and the heat diffusion effect due to the heat transfer property, the temperature rise near the fins is suppressed and prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a thermal decomposition reaction tube having a high heat transfer property by a fin provided on the inner surface of the tube and suitable as a thermal decomposition reaction tube for ethylene production.

[0002]

2. Description of the Related Art In a pyrolysis furnace for producing ethylene, a raw material fluid containing hydrocarbons such as naphtha and light kerosene is supplied to a pyrolysis reaction tube arranged in the furnace, and while flowing at high speed in the tube, By heating from the outside of the tube, olefins such as ethylene and propylene are obtained as a thermal decomposition reaction product. The thermal decomposition reaction of ethylene includes a secondary reaction of olefin (production of acetylene by dehydrogenative decomposition reaction of ethylene, deposition of free carbon by decomposition of acetylene), which lowers and produces ethylene yield. Free carbon is deposited (coking) on the inner surface of the pipe and accelerates deterioration of the pipe material due to carburization, resulting in a decrease in service life. In order to prevent the secondary reaction of olefins from being suppressed and to obtain a target product such as ethylene in high yield, it is necessary to quickly heat and raise the raw material fluid in the pipe to a predetermined reaction temperature to complete the reaction in a short time. is necessary. Therefore, the reaction tube is required to have a high heat transfer property. As a means for enhancing the heat transfer performance of the reaction tube, it has been proposed that forming fins on the inner surface of the tube is effective (JP-A-6-109392). This is to rapidly heat the pipe fluid by heating as a turbulent flow formation / uniform mixing effect of the pipe fluid by the stirring action of the fin on the pipe fluid. The effect of improving the heat transfer performance by the fins is remarkable, and it becomes possible to shorten the reaction tube length, downsize the apparatus, increase the production capacity, and the like.

[0003]

The fins formed on the inner surface of the reaction tube can greatly enhance the heat transfer performance of the tube as a fluid stirring element, but on the other hand, the rear surface of the fin (the downstream side portion of the fluid in the tube). Alternatively, fluid stagnation (vortex flow) is generated in the front surface portion (upstream side portion), and thus the pipe surface temperature of the stagnation portion easily rises. This increase in temperature promotes the formation of free carbon that accompanies the secondary reaction of the olefin in the tube reaction system and the associated generation of coking. The present invention provides an improved finned pyrolysis reaction tube for preventing the above problems associated with the formation of fins on the inner surface of the tube and for more effectively exhibiting the function of the fin as a stirring element. is there.

[0004]

A first aspect of the invention is a fin pyrolysis reaction tube for petrochemical use according to the present invention, wherein the rear side of the fin formed on the inner surface of the tube as a fluid stirring element is inclined from the top of the fin. A second aspect of the present invention, the fins on the front side and the back side of the fin have inclined surfaces, and the third aspect of the invention is
The fin formed on the inner surface of the pipe has a through hole for allowing the fluid in the pipe to flow, and the fourth invention is
It is characterized in that fins made of a material having high thermal conductivity are formed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION According to the first to third aspects of the present invention, in which the fins formed on the inner surface of the pipe are given the above-mentioned shape, as a shape effect, stagnation / vortex of the fluid on the back side or front side of the fins The reduction / elimination prevents the rise in temperature on the back side of the fins from being suppressed. Further, according to the fourth invention in which the fin is formed of a material having high thermal conductivity, the temperature rise due to the stagnation of the fluid on the back side and the front side of the fin causes the heat diffusion based on the good thermal conductivity of the fin itself. Alleviated by the effect.

1 to 6 show examples of fin shapes according to the first to third inventions. In each figure, (1) is a tubular body, (2)
Is a fin formed on the inner surface (1 ₁ ) of the pipe, and the arrow A indicates the flow direction of the fluid in the pipe (pipe axial direction). FIG.
Is an example of the first invention in which the back portion of the fin (2) has an inclined shape that descends obliquely from the top portion of the fin along the flow direction of the fluid in the pipe. By forming the back surface of the fin (2) as such an inclined surface (3), the in-pipe fluid (G) passing through the fin (2) flows along the back surface of the inclined surface (3). Compared to the case without (3),
Less fluid stagnation on the back of the fin. FIG.
Is an example of the second aspect of the invention in which the front and rear hem portions of the fin (2) are inclined surfaces (4 ₁ ) (4 ₂ ). By giving the bottom of the fin such an inclined shape, the stagnation of the in-tube fluid (G) on the front side and the back side of the fin is weakened. The inclined surface (3) of FIG. 1,
And the inclined surfaces (4 ₁ ) (4 ₂ ) in FIG.
Is formed along the longitudinal direction (perpendicular to the paper surface).

3 to 6 show an example of the third invention in which a fin (2) is provided with a through hole for allowing the fluid (G) in the tube to flow therethrough. As the through hole (fluid passage), the fin (2) in FIG. 3 has a straight hole (5 ₁ ) penetrating the skirt from the front to the back, and the fin (2) in FIG. has a through hole which is curved toward the upper portion of the front side hem portion of the rear side (5 _2). Further, the fin (2) of FIG. 5 is provided with a through hole (5 ₃ ) which is open to the front surface and the top surface thereof, and in FIG. 6, a U-shaped through hole (opened in the front surface of the fin (2) ( 5 ₄ ) are provided.

As shown in FIGS. 3 and 4, when the through holes (5 ₁ ) and (5 ₂ ) which are opened on the front surface and the back surface of the fin (2) are provided, the fin (2) extends from the front to the back. As a flow effect of the fluid flowing through the pipe, stagnation on the front surface side and the back surface side of the fin (2) is reduced and eliminated. As shown in FIG. 5, a through hole (5 ₃ ) having openings on the front surface and the top surface of the fin (2),
As shown in FIG. 6, U having both openings on the front surface of the fin (2)
When the V-shaped through hole (5 ₄ ) is provided, the flow of the fluid in the pipe occurs in the through holes (5 ₃ ) and (5 ₄ ) due to the pressure difference between the openings at both ends of the through hole. The stagnation of the fluid on the front surface side of the fin (2) is reduced. The through holes (5 ₁ ) to (5 ₄ ) are repeatedly formed at appropriate intervals in the longitudinal direction according to the length of the fin (2) as shown in FIG. 7.

The shape and size of the fins (2) are different from those of the pyrolysis reaction.
Depending on the usage conditions of the reaction tube and the tube inner diameter (about 30 to 150 mm)
It is designed appropriately. The height of the fins from the inner surface of the pipe is about 2
15mm, the back surface of the fin (2) is an inclined surface as shown in Fig. 1.
In the case of (3), the inclination angle (angle to the inner surface of the pipe) is
Approximately 15 to 75 °, the fin base is inclined (4
₁) (4_Two) And the height of the slope is the fin height
Approximately 1/5 to 1/2, with an inclination angle of approximately 15 to 75 °
May be. As shown in FIGS. 3 to 6, the through hole (5₁) ~
(5_Four), The hole diameter of the through hole is the fin height.
Approximately 1/5 to 1/2 of the distance between adjacent through holes is
It can be about 1/2 to 4 times. The hole shape is circular
The shape is not limited to a rectangular shape (square, rectangular, etc.), oval shape
A shape or any other shape is adopted.

The fin-forming material for forming the fins having the shapes shown in FIGS. 1 to 6 is various heat-resistant alloys known as tube materials for pyrolysis reaction tubes, for example, ASTM HK40.
Material (0.4C-20Ni-25Cr-Fe), HP Material (0.5C-35Ni-25Cr-Fe)
And their improved materials, or 0.5C-45Ni-30Cr-Fe, incoloy (IN) alloy (45Cr-Ni series), etc. can be used. On the other hand, the fin forming material for forming a fin with high thermal conductivity is the thermal conductivity κ of the heat-resistant alloy forming the tubular body.
^{(.. cal / cm s ℃} ) [e.g., HPM material κ: 0.056 (800 ℃),
0.061 (900 ℃), HK4M material κ: 0.057 (800 ℃), 0.063 (900
C.), HP material κ: 0.060 (800 ° C.), 0.065 (900 ° C.), IN657 material κ: 0.064 (800 ° C.), 0.069 (900 ° C.)] are preferably used. As an example of such a fin forming material, a WC-TiC-Co based cemented carbide [eg 94
WC-1TiC-5Co κ: 0.19, 84.5 WC-5TiC-13Co κ: 0.15
], Silicon carbide ceramics [eg dense SiC κ:
≧ 0.09 (780 ℃), self bonded SiC κ: ≧ 0.09 (1080 ℃)
And the like. In addition, various ferrous and non-ferrous metals (alloys), cermets, ceramics and the like having material properties such as heat resistance capable of withstanding the environment in which the pyrolysis reaction tube is used and high thermal conductivity are appropriately used. When imparting the shape as shown in FIGS. 1 to 6 to the fin formed of a material having good thermal conductivity, the thermal diffusion effect and the shape effect are superimposed,
It is possible to more effectively suppress and prevent the temperature rise of the fin and its vicinity.

The fins (2) formed on the inner surface of the tube are given various distribution forms. 8 to 10 show an example thereof. The fin (2) of FIG. 8 is an example formed as a ring-shaped fin extending in a direction substantially orthogonal to the tube axis (x), and FIG. 9 is a spiral extending in a direction inclined with respect to the tube axis (x). It is an example formed as a fin. FIG. 10 shows an example in which the ring-shaped fin (2) of FIG. 8 is provided with break points to form the interrupted fin (2). The spiral fin (2) of FIG. 9 is also interrupted if desired. Formed as a general spiral fin. The pitch of the fins (2) (distance between adjacent fins) is about 3 to 400 mm, the inclination angle of the spiral fins is about 15 ° or more, and the length of each fin in the fin having an interrupted shape as shown in FIG. An example is about 3 to 100 mm and the length of the break point is about 1 to 50 mm. In addition, it is also possible to form fins composed of projections in a dotted pattern forming a regular or random distribution pattern, and various shapes and distribution patterns of the fins (2) can be designed.

The fin (2) is formed on the inner surface of the pipe by applying, for example, powder plasma welding, TIG welding, or MIG welding according to the type of the fin-forming material used, and the fin is used as a build-up bead. It can be formed, and as an alternative method, a member (cast product, forging product, sintered product, etc.) that has been processed into the required shape is used as the fin-forming member, and this is applied to the required location on the inner surface of the pipe for welding, etc. You may make it join and fix by the method. As shown in FIGS. 3 to 6, the through holes (5 ₁ ) to
In the case of the fin (2) having (5 ₄ ), as the fin member, a member having through holes (5 ₁ ) to (5 ₄ ) and having a ring shape matching the curved surface of the pipe inner surface is manufactured. It can be formed by applying a method of joining and fixing it to the inner surface of the pipe. Further, when the fin (2) having a triangular cross section as shown in FIG. 1 is formed as a build-up bead by plasma powder welding, as shown in FIG. Is applied to the inner surface of the pipe, the welding torch (10) is inclined to the plate surface of the contact plate (11), and the beads are built up to form the fin (2) having a desired cross-sectional shape. As the contact plate (11), a heat-resistant metal plate or a ceramic plate is used, and a fin for cooling (12) or an appropriate water cooling means (not shown) is provided on the plate to heat the contact plate (11). The fins can be efficiently formed by preventing damage and adhesion of beads.

[0013]

According to the present invention, the temperature rise in the vicinity of the fins formed on the inner surface of the pipe and the occurrence of coking due to the temperature rise are prevented and prevented, and the function of the fins as a stirring element is more effectively exhibited. A high ethylene yield can be secured, carburization / deterioration of the reaction tube due to coking is suppressed and prevented, and the service life of the reaction tube is extended.
The frequency of performing the decoking work (the work of removing the deposited carbon on the inner surface of the pipe) and the shutdown of the furnace for that purpose is reduced, and it becomes possible to maintain the efficient pyrolysis operation.

[Brief description of drawings]

FIG. 1 is a sectional view in the axial direction of a tube showing the shape of fins of a metal tube for heat exchange of the present invention.

FIG. 2 is a sectional view in the tube axis direction showing the shape of fins of the metal tube for heat exchange of the present invention.

FIG. 3 is a sectional view in the tube axis direction showing the shape of fins of the metal tube for heat exchange of the present invention.

FIG. 4 is a cross-sectional view in the tube axis direction showing the shape of fins of the metal tube for heat exchange of the present invention.

FIG. 5 is a cross-sectional view in the tube axis direction showing the shape of fins of the metal tube for heat exchange of the present invention.

FIG. 6 is a sectional view in the tube axis direction showing the shape of fins of the metal tube for heat exchange of the present invention.

FIG. 7 is a front view showing the shape of fins of the metal tube for heat exchange of the present invention.

FIG. 8 is a schematic cross-sectional view in the tube axis direction showing a distribution form of fins on the inner surface of the tube.

FIG. 9 is a schematic cross-sectional view in the tube axis direction showing a distribution form of fins on the inner surface of the tube.

FIG. 10 is a schematic cross-sectional view in the tube axis direction showing a distribution form of fins on the inner surface of the tube.

FIG. 11 is a diagram showing an example of how fins are formed by welding overlay.

[Explanation of symbols]

1: tube 1 _1: inner surface 2: fins 3,4 _1, 4 _2: inclined surfaces 5 ₁ to 5 _4: through-hole (fluid passage) G: line fluid 10: welding torch 11: contact plate 12: Cooling Fins

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masamichi Hino 1-1-1, Hama, Amagasaki City, Hyogo Prefecture Kubota Technology Development Laboratory Co., Ltd. (72) Inventor Masayuki Tomita 1-1-1, Nakamiya Oike, Hirakata City, Osaka Prefecture Stock company Kubota Hirakata Factory

Claims (4)

[Claims] 1. A heat with a fin for petrochemicals, characterized in that fins are formed on an inner surface of the pipe as an agitating element for the fluid in the pipe, and a rear surface side of the fin has an inclined surface descending from the top of the fin. Decomposition reaction tube. 2. A pyrolysis reaction tube with fins for petrochemicals, characterized in that fins are formed on the inner surface of the tube as an agitating element for the fluid in the tube, and the fins on the front side and the back side have inclined surfaces. 3. A pyrolysis reaction tube with fins for petrochemicals, characterized in that fins are formed on the inner surface of the pipe as a stirring element for the fluid in the pipe, and the fins are provided with through holes for allowing passage of the fluid in the pipe. 4. A pyrolysis reaction tube with fin for petrochemistry, wherein fins made of a material having high thermal conductivity are formed on the inner surface of the tube as an agitating element for the fluid in the tube.