JPS5813600B2 - Bunkaigasutsuourono Setsuzokuhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing the diameter of a passageway for cracked gas produced when heavy hydrocarbons with a high residual carbon content are thermally decomposed.

More specifically, when producing olefins, fuel gas, fuel oil, etc. by thermally decomposing heavy hydrocarbons with a high residual carbon content such as crude oil, heavy oil, asphalt, and tar sand in a fluidized bed reactor. The present invention relates to a method for reducing the diameter of a high-temperature gas passage for guiding generated decomposed gas to a cooler in order to prevent locally generated lumps of coking material from accumulating.

When pyrolyzing heavy oil hydrocarbons with a high residual carbon content, an extremely large amount of coking material precipitates, so the tubular pyrolysis furnace used for pyrolysis of naphtha etc. cannot be used at all, and the fluidized bed is used instead. It is known that a type reactor can be used.

That is, most of the coking material produced is attached to the heat carrier particles, and can be removed by an appropriate method such as combustion.

However, it is not possible to deposit the entire amount of coking material on the particles, and a portion accumulates on the walls of the cracked gas passage.

A general method for thermally decomposing heavy hydrocarbons in a fluidized bed reactor is described, and the problems are clarified.

When raw material heavy hydrocarbons are supplied to a fluidized bed maintained at a predetermined temperature, the heavy hydrocarbons are thermally decomposed to generate cracked gas.

The decomposition temperature is 700-850℃ for olefin production.
In the case of fuel gas production, the temperature is 900°C or higher, and in the case of fuel oil production, the temperature is about 500 to 700°C.

At these decomposition temperatures, the oil is also mostly in the gaseous state.

The cracked gas passes through a space above the fluidized bed (called a freeboard), passes through a particle separator such as a cyclone to separate particles entrained in the cracked gas, is led to a cooler, and then to a fractional distillation purification system. It will be destroyed.

Caulking material buildup occurs primarily on the interior walls of piping and equipment through which hot cracked gases pass to the freeboard and cooler.

There is no buildup of caulking material after the cooler.

The thickness of the caulking material accumulated on the wall surface is not necessarily uniform, and the caulking material may accumulate locally in very thick or even irregular lumps.

Such a significant local accumulation of coking material locally narrows the cracked gas passage in a short period of time, significantly increasing the flow resistance of the cracked gas, and is therefore a serious obstacle to long-term continuous operation.

The purpose of the present invention is to prevent such significant local accumulation of caulking substances.

Such local accumulation of caulking material occurs on the narrow passage side of the connection portion when the cracked gas passes through the narrow passage from the wide passage.

That is, in the past, it was common practice to connect a narrow passage and a thick passage with a connecting curved surface in the shape of a truncated cone or two or more consecutive truncated cones, as shown in Figure 4. ,
In the conventional method of reducing the passage, the so-called contraction effect causes the turbulent flow of gas with vortices downstream of the connection between the truncated cone and the narrow passage and/or the connection between the truncated cones. A stagnation portion is generated.

Coking substances of small particle size contained in suspended form in cracked gas or substances that cause generation of coking substances (
For example, fine droplets of raw material heavy hydrocarbons, polycondensates generated while the cracked gas flows through the passage, condensed mist of heavy components in the cracked gas, etc. When it is mixed in, the residence time in that area increases, and the chance of contact with the passage wall is much greater than on walls other than the retention area, so the growth rate of the caulking material on the wall is accelerated, resulting in a large amount of caulking. This results in the accumulation of substances.

The amount of local caulking material is approximately proportional to the size of the retention area.

The size of the retention area increases as the difference in diameter between the wide passage and the narrow passage increases.

Therefore, in the case of a fluidized bed reactor, the connection to the piping for discharging the cracked gas from the freeboard is particularly problematic.

In thermal decomposition reactions, it is generally attempted to shorten the residence time in the cracked gas passage in order to suppress side reactions, but in order to meet this requirement, shortening the connecting part from the thick passage to the narrow passage results in a shortening of the residence time in the cracked gas passage. If it is thick, it will increase local caulking.

According to the method of the present invention, localized caulking can be reduced to a level that does not pose a practical problem, and the length of the connecting portion can also be made extremely short.

The present invention aims to reduce the passage of cracked gas generated when heavy hydrocarbons with a low residual carbon content are thermally decomposed at a temperature of 500°C or higher in a fluidized bed reactor. The following conditions are met: (1) The connecting curved surface is smooth over the entire surface except for the point where it joins the thick passage, and the cross-sectional area of the connecting curved surface is narrow toward the upstream end over the entire connecting curved surface. and%
On the curved surface connected to the point, the inner side of the passage (the cracked gas side)
and the radius of curvature on the upstream side of the connecting curved surface is equal to or smaller than the radius of curvature on the downstream side. (However, MA is the difference between the cross-sectional area of the connecting curved surface and the cross-sectional area of the narrow passage This is a method of connecting with a curved surface that satisfies the difference between the cross-sectional area of the thick passage and the cross-sectional area of the narrow passage.

According to the method of the present invention as described above, it is possible to extremely effectively prevent local accumulation of coking substances by substantially eliminating the portion where cracked gas remains.

The fluidized bed reactor used in the present invention is maintained at a predetermined temperature by heated particles in a suitable manner.

For example, in a two-column circulation reactor, the heating method is to blow combustion gas generated from a combustion device installed outside the heating tower into the heating tower, or to directly supply fuel and oxygen to the heating tower. Alternatively, the fluidized bed reactor is maintained at a predetermined temperature by blowing air to combust the fuel, or by blowing oxygen into the heating tower to burn the coking material adhering to the heat carrier particles.

The particles used are made of sand, refractories, or coke, and the particle size varies depending on the heating method or particle circulation method.
Approximately 04 to 10 homo is used.

The raw material heavy hydrocarbons are sprayed into fine droplets into the fluidized bed.

Heavy hydrocarbons refer to those with a residual carbon content of about 3 wt% or more, and which are not distilled no matter how high the distillation temperature is and some of them remain as residue in the pot.

Specific examples include crude oil, heavy oil, asphalt, vacuum distillation column residue oil, and bitumen.

The decomposition temperature is 500°C or higher. That is, the temperature is 500 to 700°C when the purpose is to produce fuel oil, 700 to 850°C when producing olefin, and about 900°C or more when producing fuel gas.

When reducing the passage of cracked gas in a fluidized bed reactor, the most important thing is to make the freeboard a thick passage, and the freeboard ~
This is a connection in which the piping between cyclones is a narrow passage.

The linear velocity of the decomposed gas in the pipe is usually 10 to 200 m/sec, preferably 15 to 150 m/sec, depending on the temperature and pressure at that point.

The linear velocity of the decomposed gas in the freeboard varies depending on the particle size of the particles used, but is usually about 0.1 to 4 m/see.

It is preferable to connect the thick passage to the narrow passage so that the central axes of both passages are parallel to each other.

The connecting surface must be smooth.

Smooth, as taught in geometry, means that the tangent plane at any point A on a curved surface makes point B approach point A in relation to the tangent plane at any point B near that point. A curved surface in which the tangent plane at point B and the tangent plane at point A completely match.

The connection curved surface is thick (and does not need to be smooth at the connection point with the passage.

That is, the stagnation part of the flow where the local accumulation of caulking material occurs occurs at the contraction part where the passage is narrowed, and the stagnation part does not occur at the connection point with the thick passage.

Further, it is necessary that the cross-sectional area of the connecting curved direction be uniform in the upstream direction over the entire surface of the connecting curved surface.

Furthermore, the connecting curved surface between the narrow passage and the moon point is convex on the inside of the passage (on the cracked gas side), and in the above connecting curved surface, the radius of curvature of the point on the upstream side is always equal to the radius of curvature on the downstream side. or small.

That is, between the narrow passage and the % point, the radius of curvature must be constant or gradually decrease toward the upstream side.

Upstream here means the direction of the thick passage.

The reason for this provision is as follows.

The stagnation portion in the contraction section becomes larger as the velocity of the gas is faster and the velocity change due to the contraction of the passage is more severe.

Therefore, by rapidly shrinking the passage where the cross-sectional area of the passage is relatively large, and by gradually reducing the passage as the cross-sectional area becomes smaller, the stagnation area can be made smaller, and the length of the connecting part can be reduced. can be made shorter.

As far as the connection curved surface between the thick passage and the % point is concerned, it is not necessarily necessary that it be convex inward.

Although it is necessary to be smooth and have a large cross-sectional area at the upstream end, it may be concave inward.

For example, a curved surface that is convex on the inner side of the eight passages as shown in Figure 12, a curved surface that is concave on the inner side of the passage as shown in Figure 3, or a mixture of both can also be used. .

The present invention will be explained below with reference to Examples.

Example 1 Heavy hydrocarbons were thermally decomposed in a fluidized bed reactor as shown in Figure 1.

This apparatus is, for example, a two-column particle circulation type fluidized bed reactor as proposed in Japanese Patent Publication No. 45-36289.

The heat carrier particles are heated in the heating tower (2) and transferred to the reaction tower (2), and the particles in (2) are further transferred to (2), thus circulating through both columns.

The particles have an average value of 0. 8 mm coke particles were used.

In the reaction tower, steam (2) is blown into the bottom and sides of the tower to fluidize the particles.

The raw material is blown into the reaction tower from step (1) and is thermally decomposed in the presence of steam.

The reaction temperature was 750° C. and the pressure was 0.2 kg/c shoulder G.

The raw material was a vacuum distillation column residual oil of Middle East crude oil, which had a needle size of 80 to 100 and a residual carbon content of 23 wt%.

Original supply amount is 150ky/Hr, steam amount is 38
It was 0 kV'Hr.

The decomposition product gas is transferred from the reaction tower free board■ to the cyclone■
, passed through the cooler ■ and led to the distillation and purification system.

As for the dimensions of the passage, the inner diameter of the reaction tower freeboard is 600 mm.
The inner diameter of the pipe between the freeboard and the cyclone was 133 mm.

The freeboard part of the reaction tower was made into a thick pipe, and the piping between the freeboard and the cyclone was made into a thin pipe and connected with the dimensions shown in Figure 2.

That is, the tube axes of the narrow passage and the thick passage are made to coincide, and in the cross-sectional figure including the tube axis, the radius is 1000 mm and 350 mm.
They are connected by a smooth curved surface forming two arcs of m.

However, the connection between the curved connection surface and the thick pipe is not smooth.

Continuous operation was carried out for 410 hours under the apparatus configuration and reaction conditions as described above.

No difficulties occurred during driving.

After a normal shutdown, we dismantled it and inspected the accumulation of caulking material. As a result, we found that a uniform thickness of approximately 20 cm of caulking material had accumulated on the freeboard, the connecting curved surface, and the wall of the pipe between the freeboard and the cyclone. However, no accumulation of caulking material that would locally narrow the passageway was observed.

Comparative Example The freeboard of the reaction tower was made into a thick pipe, and the freeboard and cyclone were made into thin pipes, and both were connected in the shape and dimensions shown in FIG. 4.

That is, the cross-sectional figure including the central axis has a connection that forms a figure consisting of two trapezoids.

The operation was carried out with the other equipment configurations and raw material reaction conditions being the same as in Example 1, but due to an abnormal increase in the pressure of the reaction tower, the
The operation was stopped in time.

As a result of disassembly and inspection, it was found that there was local accumulation of caulking material near the thin pipes and the connecting surfaces, and the opening diameter of the pipe was approximately 50 miφ.

That is, the opening area was reduced to about 14% of the initial cross-sectional area of the thin tube.

The average thickness of the caulking material in other parts of the narrow tube was about 5 mm.

[Brief explanation of drawings]

Figure 1 is a block diagram of the fluidized bed reactor used in Example 1 and Comparative Example; Figure 2 is a diagram of the curved surface connecting the reaction tower freeboard and the piping between the freeboard and the cyclone in Example 1; FIG. 3 is a cross-sectional view showing another example of the connection curved surface according to the present invention; FIG. 4 is a cross-sectional view showing another example of the connection curved surface according to the invention; It is a diagram showing the configuration and dimensions of a curved surface connecting a freeboard and a pipe between a cyclone, and is a cross-sectional view including the central axis.

Claims (1)

[Claims] 1. In order to reduce the passage of cracked gas generated when heavy hydrocarbons with a large residual carbon content are thermally decomposed at a temperature of 500°C or higher in a fluidized bed reactor, a thick passage and a narrow passage are used. and the passage under the following conditions: (1) The connecting curved surface is smooth over the entire surface except for the joint point with the thick passage, and the cross-sectional area of the connecting curved surface is narrow toward the upstream end over the entire surface of the connecting curved surface, (2) It is thin passage and 1
/ The connecting curved surface with the three points is convex on the inner surface side of the passage (the cracked gas side), and the radius of curvature on the upstream side of the connecting curved surface is equal to or smaller than the radius of curvature on the downstream side. A point is a point where the difference between the cross-sectional area of the connecting curved surface and the cross-sectional area of the narrow passage is 1/3 times the difference between the cross-sectional area of the thick passage and the cross-sectional area of the narrow passage). Method.