JPH0447719B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention produces ethylene,
The present invention relates to a hydrocarbon pyrolysis tube suitable for producing propylene and other useful olefins. [Background technology and its problems] Generally, a pyrolysis furnace with a built-in pyrolysis tube is used to produce olefins by pyrolysis of hydrocarbons.
After heating the hydrocarbons to 800-950℃ and thermally decomposing them,
A rapid cooling method is used. In this case, various measures have been taken to increase the efficiency of heat transfer to the fluid within the pyrolysis tube, such as providing fins or ridges on the inner or outer surface of the pyrolysis tube, or making the tube elliptical. In addition, in order to improve the yield of olefin, especially the yield of useful ethylene, efforts have been made to shorten the residence time in the pyrolysis tube and cool it as quickly as possible. However, if you try to improve the conversion rate by tightening the reaction conditions, the coke produced in the pyrolysis tube will adhere to the inside of the pyrolysis tube, and it will be necessary to remove the adhering coke frequently. It has been desired to develop a pyrolysis tube that can improve the efficiency of the entire pyrolysis process. [Objectives of the Invention] The objects of the present invention are to achieve a high yield of olefin, less coke precipitation in the pyrolysis tube, a long period of continuous operation, and shorten the time required for decoking, so that the entire pyrolysis equipment can be improved. The object of the present invention is to provide a pyrolysis tube that can be used for pyrolysis of hydrocarbons and can improve the operating rate of the pyrolysis tube. [Means and effects for solving the problems] The present invention provides a hydrocarbon pyrolysis tube used when producing olefin by pyrolyzing naphtha or heavy gas oil while raising the temperature to 800 to 950°C. , its average inner diameter is 15 to 45 mm, and the shape of the inner surface of the tube has 5 to 10 grooves in the cross section that are continuous semicircular arc-shaped unevenness to form a wave shape, and these grooves extend along the length of the tube. The purpose is to achieve the above object by forming a helical shape with an inclination angle of 5 to 20 degrees in the direction. Therefore, since the transfer efficiency can be increased, the yield of olefin can be improved, and the precipitation of coke in the pyrolysis tube is slight, so that the operating efficiency of the entire pyrolysis apparatus can be dramatically improved. [Example] An example of the hydrocarbon pyrolysis tube according to the present invention will be described in detail with reference to the drawings. This embodiment is shown in FIGS. 1 and 2, and FIG. 3 shows a schematic configuration of a pyrolysis apparatus used in this embodiment. In FIG. 3, the pyrolysis furnace 10 has a plurality of burners 12, for example, 12 burners.
It is equipped with a straight pyrolysis tube 14. The inlet sides of these pyrolysis tubes 14 are connected by an inlet header 16, and the outlet sides are connected by four outlet headers 18 each. A quencher 22 is connected outside the furnace. Hydrocarbons and steam are supplied to the raw material supply pipe 20, respectively, and these raw materials are supplied to the raw material supply pipe 20.
The heat is supplied to the inlet header 16 after being preheated by preheaters 24 and 26 provided in the respective parts. As shown in FIG. 1, the cross section of each of the pyrolysis tubes 14 has a plurality of grooves 14A in which the inner surface of the tube has a continuous semicircular arc-shaped unevenness to form a waveform. 14A, as shown in FIG.
It is formed in a spiral shape with an inclination angle α and a pitch P in the longitudinal direction of the pipe. Pyrolysis tube 14 having such a shape
The specific structure is made of ASTM standard HP made of a nickel-chromium alloy, and the outer diameter D ₀ = 47.6 mm, the diameter between the groove bottoms d ₁ = 32.35 mm, and the diameter between the protrusions d ₂ = 23.1 mm. Therefore, average inner diameter D _A = 27.7 mm, groove depth h =
4.62 mm, minimum wall thickness t = 7.63 mm, number of grooves is 8, groove inclination angle α = 10 degrees, groove pitch P = 400 mm,
The length L of each straight pyrolysis tube (see Figure 3) was 11 m, and 12 of these pyrolysis tubes 14 were used to carry out pyrolysis. Here, the average inner diameter D _A is the value obtained by subtracting twice the average value of the maximum (t + h) and minimum (t) wall thickness from the outer diameter D ₀ of the pyrolysis tube 14, or the diameter between the groove bottoms d ₁ and the inter-convex diameter _d2 .
In addition, the actual inner circumference S = 124 mm and the average inner circumference C =
When the area expansion ratio S/C is calculated from π・D _A =86.978, S/C=1.426, which shows that the contact area of the raw materials has increased significantly. As raw materials for hydrocarbons, naphtha, baqueum, gas oil (vacuum gas oil) and hydrodesulfurized gas oil having the properties shown in Table 1 were used.

【table】

[Table] By continuing thermal decomposition under these conditions,
Coking occurred inside the pyrolysis tube 14, the pressure loss inside the tube increased, the heat transfer effect of the pyrolysis tube 14 decreased, and the outer surface temperature of the pyrolysis tube 14 increased.
When this temperature reaches 1092℃, pyrolysis tube 1
Considering the strength and life of No. 4, thermal decomposition was interrupted and decoking was performed. Since there is a correlation between the outer surface temperature limit of the pyrolysis tube 14 and the pressure loss inside the pyrolysis tube 14, a specific value of increase in pressure loss is used as a guideline for stopping pyrolysis, and when this specific value is used. Table 3 shows the values for the period during which continuous thermal decomposition operation is possible.

[Table] The yield of the thermal decomposition product in this case is also shown in Table 4 in comparison with the comparative example. Here is a comparative example:
Naphtha was pyrolyzed under the same conditions as in the previous example, except that a smooth circular tube with an outer diameter of 39.9 mm and an inner diameter of 26.9 mm and concentric inner and outer diameters was used as the pyrolysis tube, and the surface temperature of the pyrolysis tube was 1092 degrees. When it reached , decoking was performed.
The time required for this decoking was approximately 10 hours. In this case, the period during which continuous operation was possible was 13 days.

[Table] From the above examples and comparative examples, it is clear that according to the pyrolysis method using the pyrolysis tube 14 of the present invention, coking can be significantly suppressed and the operating rate of the entire pyrolysis equipment can be improved. It can be seen that the yield of olefins, especially ethylene, can be improved. Although the numerical value of these improvements in yield is small, since the amount of oil passed is large, the economic effect is large. Next, the groove inclination angle of the pyrolysis tube was determined for the case where naphtha having the same properties as in the above example was used as the feedstock hydrocarbon, the pyrolysis conditions were the same, and the operation was performed to obtain the same yield of pyrolysis products. Table 5 shows the pressure loss, continuous operation period, and decoking time as parameters. Note that the time required for decoking is the time required to flow steam at a temperature of 1000° C. into the pyrolysis tube to perform a water gasification reaction and remove coke inside the tube.

〔Effect of the invention〕

The present invention is advantageous in that it has a high yield of olefin, less coke precipitation in the pyrolysis tube, a long period of continuous operation, and can shorten the time required for decoking, improving the operating rate of the pyrolysis equipment as a whole. It has a good effect.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view showing one embodiment of the hydrocarbon pyrolysis tube according to the present invention, and FIG.
FIG. 3 is a schematic developed view of the inner surface of the pyrolysis tube showing the shape of a single groove in the pyrolysis tube, and FIG. 3 is a schematic configuration diagram of the pyrolysis furnace. 10...Pyrolysis furnace, 14...Pyrolysis tube, 14A
... Groove, 20 ... Raw material supply pipe.

Claims (1)

[Claims] 1. In a hydrocarbon pyrolysis tube used to produce olefin by thermally decomposing naphtha or heavy gas oil while raising the temperature to 800 to 950°C, the average inner diameter is 15 to 45 mm, and the inner surface of the tube is The cross section has 5 to 10 corrugated grooves with continuous semicircular irregularities, and these grooves are formed in a spiral shape with an inclination angle of 5 to 20 degrees in the longitudinal direction of the tube. A hydrocarbon pyrolysis tube characterized by: