JP2021107761A - Thermal decomposition pipe including fluid stirring element - Google Patents

Abstract

To provide a thermal decomposition pipe that can reduce a pressure loss while exerting effect of stirring internal fluid of a pipe.SOLUTION: A thermal decomposition pipe 10 includes a stirring element 20, in which one or more fluid stirring elements are formed while projecting inward at an inner surface of the pipe. The stirring element includes: a first projection 21 extending along the inner surface of the pipe and helically inclined relative to a pipe axis; and a second projection 25 inclined at an angle different from the first projection and connecting first projections to each other substantially or virtually.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pyrolysis tube used in a pyrolysis reaction furnace for producing ethylene or the like, and more specifically, a pyrolysis tube in which a stirring element for enhancing the stirring action of the fluid in the pipe is projected from the inner surface of the pipe. It is about.

For olefins such as ethylene and propylene, a raw material fluid containing hydrocarbons (naphtha, natural gas, ethane, etc.) is circulated at high speed through an externally heated thermal decomposition tube, and the raw material fluid is heated to the reaction temperature range for thermal decomposition. Is generated by.

In order to carry out the pyrolysis reaction efficiently, it is important to heat and raise the temperature of the raw material fluid that flows at high speed to the radial center of the pipeline to the thermal decomposition reaction temperature range in a short time, and to avoid overheating as much as possible. be. Overheating of the raw material fluid causes excessive lightening of hydrocarbons (production of methane, free carbon, etc.) and polycondensation reaction of decomposition products, resulting in a large decrease in the yield of the target product. In addition, caulking (deposition of free carbon on the inner surface of the pipe) is promoted, which leads to a decrease in the heat transfer coefficient of the pipe body. Therefore, it becomes necessary to carry out decoking work frequently, and the operating time is reduced.

Therefore, a ridge is provided on the inner surface of the pyrolysis pipe as a stirring element for the flowing fluid (see, for example, Patent Document 1). In Patent Document 1, the ridges are formed so as to spirally swivel with respect to the pipe axis. Then, the fluid flowing at high speed is agitated by the ridges to promote heat transfer, and is rapidly heated to a high temperature, and the thermal decomposition is completed in a short time. This suppresses the occurrence of over-decomposition and coking due to overheating, and by improving the heat transfer efficiency of the pyrolysis tube, it is possible to lower the heating temperature of the pyrolysis tube and improve the service life of the pyrolysis tube. The effect is brought about.

Japanese Unexamined Patent Publication No. 2008-249249

However, the spiral ridges improve the agitation of the fluid and at the same time increase the pressure loss of the fluid in the pipe. An increase in pressure drop can lead to a decrease in olefin yield. Therefore, there is a demand for a pyrolysis tube with low pressure loss.

An object of the present invention is to provide a pyrolysis tube capable of reducing pressure loss while having a stirring effect of a fluid in a tube.

The pyrolysis tube provided with the stirring element of the present invention
A pyrolysis tube formed by inwardly projecting one or more fluid stirring elements on the inner surface of the tube.
The stirring element is
A first ridge extending along the inner surface of the pipe and spirally inclined with respect to the pipe axis.
A second ridge having a different inclination angle from the first ridge, and a second ridge that substantially or virtually connects the first ridges to each other.
including.

The pyrolysis tube provided with the stirring element of the present invention
A pyrolysis tube formed by inwardly projecting one or more fluid stirring elements on the inner surface of the tube.
The stirring element is
On the inner surface of the pipe, a first ridge orthogonal to the pipe axis,
A second ridge having an inclination angle different from that of the first ridge with respect to the pipe axis, and a second ridge that substantially or virtually connects the first ridges to each other.
including.

The second ridge may be configured to connect the edges of the first ridge to each other.

The second ridge may be configured to connect portions other than the edge of the first ridge.

The height H1 of the first ridge can be equal to the height H2 of the second ridge.

The height H1 of the first ridge and the height H2 of the second ridge can be H2 / H1 ≧ 1/2.

The second ridge may be configured to connect the first ridges in parallel with the pipe axis direction.

The second ridge may be configured to connect the first ridges so as to be orthogonal to the first ridge.

It is desirable that the first ridge section in which the first ridge is formed has a length equal to or longer than the second ridge section in which the second ridge is formed.

The first ridge section may be 60% to 80% of the total of the first ridge section and the second ridge section.

According to the pyrolysis tube of the present invention, the fluid is agitated by the first ridge. The fluid that has passed through the first ridge becomes a turbulent flow, but the pressure loss can be reduced by changing the direction of the flow and rectifying the fluid by the second ridge having a different angle from the first ridge. As a result, it is possible to prevent an increase in pressure loss, improve the yield of olefins, and suppress the occurrence of caulking due to overdecomposition, while providing a stirring effect and ensuring heat transfer efficiency.

FIG. 1 is a developed view of a pyrolysis tube in which a stirring element is formed according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. FIG. 3 is a developed view of a pyrolysis tube in which different forms of stirring elements are formed. FIG. 4 is a developed view of a pyrolysis tube in which ridges having a different form are formed. FIG. 5 is an explanatory diagram of the test pyrolysis tube used in the examples. FIG. 6 is a developed view of a thermal decomposition tube of a comparative example.

Hereinafter, the thermal decomposition tube 10 of the present invention will be described with reference to the drawings. Although the pyrolysis pipe 10 shown in the figure is a straight pipe, in general, the pyrolysis pipes 10 made of straight pipes are connected to each other by a bent bend pipe and deployed in a pyrolysis furnace in a meandering shape. It receives heat from the outside of the pipe and thermally decomposes the fluid flowing inside.

FIG. 1 is a developed view showing an embodiment of the pyrolysis tube 10 of the present invention, and FIG. 2 is an enlarged cross-sectional view taken along the line II-II of FIG. For convenience of explanation, the left side of the paper in FIG. 1 is the upstream side, and the right side is the downstream side.

The pyrolysis tube 10 can be formed from a heat-resistant alloy material and contains 25Cr-Ni (SCH22), 25Cr-35Ni (SCH24), Incoloy (trade name), or Al: 6.0% by mass as an upper limit. An alloy can be exemplified. Of course, the material of the pyrolysis tube 10 is not limited to these, and various heat-resistant alloy materials that can withstand a high-temperature usage environment and have the required performance can be used.

The pyrolysis tube 10 is formed with a stirring element 20 that projects inward from the inner surface of the tube. More specifically, the stirring element 20 can be a first ridge 21 and a second ridge 25 having a different angle from the first ridge 21.

The first ridge 21 mainly agitates the fluid, and the second ridge 25 mainly rectifies the fluid.

In FIG. 1, the first ridge 21 can have a spiral shape that is inclined at an angle θ1 from the upstream side to the downstream side with respect to the plane orthogonal to the pipe axis. On the inner surface of the pipe, the section in which the first ridge 21 is formed is referred to as the first ridge section 22. Then, the first ridge 21 is connected to the second ridge 25 at an end edge or a portion other than the end edge. The second ridge 25 is a ridge having an angle θ2 different from the angle θ1 of the first ridge 21. On the inner surface of the pipe, the section where the second ridge 25 is formed is referred to as the second ridge section 26. A first ridge 21 is formed on the downstream side of the second ridge 25, and the second ridge 25 is connected to the first ridge 21.

As shown in FIG. 1, the second ridge 25 may have a form in which the edges of the first ridge 21 are connected to each other, or the portions other than the edges of the first ridge 21 (23, 24) are connected to each other. May be in the form of connecting (see FIGS. 3 and 4). As shown in FIG. 1, it is desirable that the first ridge 21 and the second ridge 25 are substantially connected, but between the first ridge 21 and the second ridge 25. A gap may be provided in the ridge 25 so that the extension line of the second ridge 25 is virtually connected to the first ridge 21.

The inclination angle θ1 of the first ridge 21 is preferably 85 ° or less, and preferably 30 ° or less. It is desirable that the inclination angle θ1 of the ridge 21 is 15 ° or more. As shown by reference numeral 23 in FIG. 3, the first ridge 21 may have a form orthogonal to the pipe axis with θ1 = 0 °. If the inclination angle θ1 is too small, stagnation is likely to occur on the downstream side of the ridge 21, but as the inclination angle θ1 is too small, the inclination of the first ridge 21 with respect to the pipe axis is large, so that the flowing fluid is agitated and turbulent. The generation effect can be enhanced.

The inclination angle θ2 of the second ridge 25 is different from the inclination angle θ1 of the first ridge 21, and for example, as shown in FIGS. 1, 3 and 4, the second ridge 25 is a pipe. The angle parallel to the axis (θ2 = 90 °) can be set. The inclination angle θ1 of the first ridge 21 (23, 24) and the inclination angle θ2 of the second ridge 25 both have an elevation angle of 0 ° or more and 90 ° or less in the same direction with respect to the plane orthogonal to the pipe axis. , Θ1 is preferably formed so as to have an angle smaller than θ2.

The first ridge 21 and the second ridge 25 can be in a continuous form, but may be in an intermittent form. FIG. 4 shows an embodiment in which the first ridge 21 is an intermittent ridge 24, 24, and the second ridge 25 is a portion other than the edge of the intermittent first ridge 24, 24. I'm connected.

The distance I between the first ridges 21 can be about 20-400 mm when the inner diameter of the pipe is 30-150 mm. The first ridge 21 in FIG. 1 has a single spiral shape, but a plurality of spiral shapes may be provided in parallel or at different inclination angles.

When comparing the lengths of the first ridge section 22 and the second ridge section 26, as shown in FIG. 1, it is preferable that the first ridge section 22 has a length of the second ridge section 26 or more. Is. Desirably, the ratio occupied by the first ridge section 22 (first ridge section 22 / (first ridge section 22 + second ridge section 26)) is preferably 50% or more, and preferably 60% or more. , 65% or more is more desirable. This is because the stirring effect of the first ridge 21 is more important than the rectifying effect of the second ridge 25. On the other hand, in order to exert the rectifying effect of the second ridge section 26, the ratio occupied by the first ridge section 22 is preferably 80% or less, and preferably 70% or less.

It is desirable that the height H1 of the first ridge 21 and the height H2 of the second ridge 25 shown in FIG. 2 are about 1 / 60-1 / 10 of the inner diameter of the pipe. If the height H1 of the first ridge 21 is lower than 1/60 of the inner diameter of the pipe, there is a possibility that the effect of agitating the fluid and generating turbulence cannot be sufficiently exhibited. Further, if the height H2 of the second ridge 25 is lower than 1/60 of the inner diameter of the pipe, there is a possibility that the rectifying effect of the fluid cannot be sufficiently exhibited. Further, when the height H1 of the first ridge 21 and the height H2 of the second ridge 25 are higher than 1/10 of the inner diameter of the pipe, the first ridge 21 and the second ridge 25 allow the fluid to flow. There is a risk that the pressure loss will increase due to hindrance, and further, fluid will stay on the downstream side of the first ridge 21 and the second ridge 25, and overdecomposition and cork will easily accumulate. Therefore, it is desirable that the height H1 of the first ridge 21 and the height H2 of the second ridge 25 satisfy the above provisions. It is desirable that the height H1 of the first ridge 21 and the height H2 of the second ridge 25 are the same in terms of stirring and rectifying effects, and the first ridge 21 and the second ridge 25 are also equal. It is desirable that the heights are the same in terms of simplifying the formation of. As used herein, "equivalent" means that the values measured by one of ordinary skill in the art are within an acceptable margin of error. Of course, the value also depends on the measurement method. In addition, "equivalent" includes a range of up to 20%, 10%, 5%, or 1% of the measured value.

The first ridge 21 and the second ridge 25 can also make the height H1 of the first ridge 21 higher than the height H2 of the second ridge 25. In this case, it is preferable that the height H2 of the second ridge 25 is 1/2 times the height H1 of the first ridge 21, that is, H2 / H1 ≧ 1/2. The fluid that has been agitated by the first ridge 21 and has become a turbulent flow is rectified by the second ridge 25, but is rectified by forming the second ridge 25 slightly lower than the first ridge 21. The pressure loss at the time can be reduced. Further, the height H1 of the first ridge 21 may be twice or more (H1 ≧ 2 × H2) the height H2 of the second ridge 25. By increasing the height H2 of the second ridge 25, the rectifying effect can be enhanced, and as a result of increasing the specific surface area of the second ridge 25, the heat transfer coefficient can be improved.

The first ridge 21 and the second ridge 25 are efficiently formed as a build-up bead by, for example, a build-up welding method such as powder plasma welding (PTA welding), MIG welding, TIG welding, and laser welding. Can be done. Of course, the first ridge 21 and the second ridge 25 can be manufactured integrally with the pyrolysis pipe 10 by extrusion processing.

The first ridge 21 and the second ridge 25 can be formed from the same type of heat-resistant alloy material as the above-mentioned pyrolysis tube 10, but are not limited thereto.

When the fluid is circulated through the pyrolysis pipe 10 in which the first ridge 21 and the second ridge 25 are formed as the stirring element 20 as described above, the fluid becomes the first ridge 21 as shown by the arrow A in FIG. The flow is spirally swirled along the first ridge 21 due to the stirring action. As a result, the fluid is agitated to the radial center of the pipeline and can be quickly heated and heated. Further, the fluid that has swirled and partially becomes a turbulent flow hits the second ridge 25 as shown by an arrow B in FIG. 1, the direction of the flow is changed, and the fluid is rectified in the direction of the pipe axis, thereby causing a pressure loss. It can be reduced. Then, as shown by an arrow C in FIG. 1, it is again agitated by the first ridge 21 on the downstream side.

As a result, the thermal decomposition tube 10 of the present invention can suppress an increase in pressure loss while rapidly heating and raising the temperature of the raw material fluid to the radial center of the pipeline to the thermal decomposition reaction temperature range, and the yield of the target product can be obtained. Improvements can be achieved.

The description of the above-described embodiment is for explaining the present invention, and should not be construed as limiting or reducing the scope of the invention described in the claims. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

As shown in FIG. 5, the pyrolysis tube 10 of the invention example having a run-up section 31 of 1.6 m on the upstream side and a length of 0.6 m shown in FIG. 1 on the downstream side, or the length shown in FIG. A test pyrolysis tube 30 connected to a 0.6 m pyrolysis tube 40 was prepared, and a fluid was circulated to measure pressure loss (kPa), outlet temperature (° C.), and heat exchange amount (kW). Compared. The inner diameter D of the pyrolysis tube 10 is 40 mm for Invention Examples 11 to 16 and Comparative Example 11 shown in Table 1, and 90 mm for Invention Examples 21 to 23 and Comparative Example 21 shown in Table 2.

As shown in FIG. 1, in the thermal decomposition tube 10 of the invention example, the first ridge 21 having a continuous spiral shape as a stirring element inside and the second ridge 21 having a different inclination angle from the first ridge 21 are different from each other. It forms a ridge 25. As shown in Table 1, the height H1 of the first ridge 21 and the inclination angle θ1 of Invention Examples 11 to 16 are the same, but the height H2 of the second ridge 25, the inclination angle θ2, and the second ridge The height of is changing. As shown in Table 2, in Invention Examples 21 to 23, the height H1 and the inclination angle θ1 of the first ridge 21 are also changed. Further, in the example of the invention, the ridges 21 and 25 are formed as shown in Tables 1 and 2 "total of the first ridge section, total of the second ridge section, and the ratio occupied by the first ridge section", respectively. The length of the section is changed. For example, in Invention Example 12, the first ridge section 22 in which the first ridge 21 is formed is 0.34 m, and the second ridge section 26 in which the second ridge 25 is formed is 0.26 m. The ratio occupied by one ridge section 22 is 0.34 / 0.6 = about 56.7%. Each of the ridges 21 and 25 has a semicircular cross section and a width of 7.0 mm. The ratio of the height of the first ridge 21 and the second ridge 25 to the inner diameter D (H1 / inner diameter D, H2 / inner diameter D), and the second ridge 25 with respect to the height H1 of the first ridge 21. The ratio of height H2 (H2 / H1) is also shown in Tables 1 and 2.

As shown in FIG. 6, the thermal decomposition pipes 40 of Comparative Examples 11 and 21 have only one spiral first ridge 21 formed therein. The cross section of the first ridge 21 is semi-circular.

While heating the test pyrolysis tube 30 having the above configuration so that the wall surface is constant at 1000 ° C., the fluid consisting of 70% by weight of ethane and 30% by weight of water vapor is heated to 700 ° C., and the inflowing mass flow rate is 0. It was supplied so as to be 2104 kg / s. The results are shown in Table 1 above.

With reference to Tables 1 and 2, it can be seen that the pressure loss of the invention example was significantly smaller than that of the comparative example, although the outlet temperature and the amount of heat exchange were substantially the same. This is because the first ridge 21 provided as the stirring element 20 is provided with the second ridge 25 having at least a different inclination angle and a different height and formation section, so that the turbulence caused by the first ridge 21 This is due to the rectification of the flow (arrow B in FIG. 1). Further, since the pressure loss can be reduced while having a stirring effect and ensuring the same heat transfer efficiency, the yield of olefin can be improved and the occurrence of caulking due to overdecomposition can be suppressed.

Next, the invention examples are compared. Comparing Invention Examples 11 to 13, the pressure loss is slightly increased by increasing the ratio occupied by the first ridge section 22. However, while obtaining the stirring effect by increasing the ratio occupied by the first ridge section 22, the agitated fluid is rectified by the second ridge 25, so that the suitable outlet temperature and heat exchange amount are obtained. It can be seen that can be secured. Therefore, it is desirable that the ratio occupied by the first ridge section 22 is 50% or more.

Comparing Invention Examples 11 and 16, and Invention Examples 21 to 23, which have different heights H2 of the second ridge 25, the higher the height H2 of the second ridge 25, the larger the pressure loss. , Suitable outlet temperature and heat exchange amount can be provided. This is because the second ridge 25 has an appropriate height, so that an effective rectifying effect can be exhibited. With reference to Invention Example 15, the ratio of the height of the second ridge 25 to the first ridge 21 is preferably 0.5 or more (H2 / H1 ≧ 1/2).

10 Pyrolysis tube 20 Stirring element 21 1st ridge 25 2nd ridge

Claims (10)

A pyrolysis tube formed by inwardly projecting one or more fluid stirring elements on the inner surface of the tube.
The stirring element is
A first ridge extending along the inner surface of the pipe and spirally inclined with respect to the pipe axis.
A second ridge having a different inclination angle from the first ridge, and a second ridge that substantially or virtually connects the first ridges to each other.
including,
Pyrolysis tube. A pyrolysis tube formed by inwardly projecting one or more fluid stirring elements on the inner surface of the tube.
The stirring element is
On the inner surface of the pipe, a first ridge orthogonal to the pipe axis,
A second ridge having an inclination angle different from that of the first ridge with respect to the pipe axis, and a second ridge that substantially or virtually connects the first ridges to each other.
including,
Pyrolysis tube. The second ridge connects the edges of the first ridge to each other.
The pyrolysis tube according to claim 1 or 2. The second ridge connects parts other than the edge of the first ridge.
The pyrolysis tube according to claim 1 or 2. The height H1 of the first ridge is equivalent to the height H2 of the second ridge.
The thermal decomposition tube according to any one of claims 1 to 4. The height H1 of the first ridge and the height H2 of the second ridge are H2 / H1 ≧ 1/2.
The thermal decomposition tube according to any one of claims 1 to 4. The second ridge connects the first ridges in parallel with the pipe axis direction.
The thermal decomposition tube according to any one of claims 1 to 6. The second ridge connects the first ridges to each other so as to be orthogonal to the first ridge.
The thermal decomposition tube according to any one of claims 1 to 6. The first ridge section in which the first ridge is formed is longer than the second ridge section in which the second ridge is formed.
The thermal decomposition tube according to any one of claims 1 to 8. The first ridge section is 60% to 80% of the total of the first ridge section and the second ridge section.
The thermal decomposition tube according to claim 9.

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