JPS5838472B2 - Method for transferring gaseous catalytic cracking products of heavy oil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for transferring gaseous catalytic cracking products of heavy oil without coking.

Gaseous decomposition products obtained by catalytically cracking heavy oils such as coal tar, shale oil, pitch, heavy oil, asphalt, etc. contain reactive components and high boiling point substances and are extremely susceptible to coking.

Coking is particularly likely to occur on the inner wall surface of the transfer pipe from the cracking reactor outlet or the cyclone outlet in the cracking reactor to the next process inlet, and as a result, the resulting coke-like substance accumulates and blocks the transfer pipe. The operation of the cracking reactor must be stopped.

Conventionally, methods have been used to keep the transfer pipe warm so that the temperature does not drop significantly below the decomposition reaction temperature, or to form a liquid film on the transfer pipe with light oil or the like to suppress coking on the pipe wall.

However, these conventional methods cannot prevent high boiling point substances in the gaseous decomposition products from condensing and depositing on the walls of the transfer pipe.

The above-mentioned high boiling point substance is a reaction active component and its secondary reaction product or undecomposed heavy oil, which exists in the form of steam or mist, and is denatured to become a coke-like substance.

The present invention relates to a method and apparatus for transferring gaseous catalytic cracking products of heavy oil, characterized in that the temperature of the transfer pipe wall is maintained at 540°C to 630°C.

When the transfer tube wall temperature is 540° C. or lower, high-boiling substances in the gaseous catalytic cracking product rapidly condense and adhere to the transfer tube wall, causing coking.

On the other hand, if the transfer pipe wall temperature is 630° C. or higher, the secondary reaction of the reactive components in the gaseous catalytic cracking product will proceed, making it easier to cause coking.

Therefore, it is necessary to maintain the temperature of the transfer pipe wall at 540°C to 630°C.

Coking as described above is affected by the gas flow rate as described later, so the temperature of the transfer pipe wall should be set between 560°C and 58°C.
Preferably, the temperature is maintained at 0°C.

The transfer pipe wall can be heated from the inside by, for example, floating and scattering high-temperature solid particles in the upper part of the reactor to exchange heat with the gaseous catalytic decomposition products, and passing the gaseous decomposition products with increased sensible heat into the transfer pipe. Can be done.

It is also possible to heat the transfer pipe from the outside by making the transfer pipe a double pipe type and exchanging heat with a high-temperature heat medium, or by wrapping it around an electric heater transfer pipe.

While controlling the temperature of the transfer pipe wall as described above, the flow rate of the gaseous catalytic cracking product is set to 20 m/sec or more, preferably 4 m/sec.
Maintaining the speed at 5 m/sec or more is advantageous for preventing caulking.

When the gas flow rate is lower than 20 m/sec, the boundary film between the tube wall and the gas fluid becomes thick, and the high boiling point substance is likely to condense and adhere to the inside of the transfer tube.

Furthermore, if the gas flow rate is made too high, erosion of the transfer pipe becomes large and pressure loss in the pipe becomes high.As a result, it becomes necessary to increase the pressure of the reactor, leading to an increase in equipment cost.

Therefore, the upper limit of the gas flow rate is preferably 120 m/sec or less.

The gas flow rate is adjusted by adjusting the shape, mainly the cross-sectional area, of the transfer tube depending on the flow rate of gas flowing from the reactor to the next step in a steady state.

In other words, if the cross-sectional area of the transfer tube is made smaller, the gas flow rate becomes faster, and if the cross-sectional area is made larger, the gas flow rate becomes slower.

If it is necessary to increase or decrease the gas flow rate in a part of the transfer pipe, it is preferable to make that part a tapered pipe.

In particular, the downstream end of the transfer pipe also serves as the inlet of the next process equipment, such as a distillation column, so the downstream end of the transfer pipe is shaped like a tapered pipe with a constriction angle within the range of 2° to 7°. In addition, by setting the ratio of the cross-sectional area of the upstream end of the tapered pipe to the cross-sectional area of the downstream end of the tapered pipe to 1.3 to 6.0, the backflow of gaseous catalytic cracking products due to the generation of swirling flow at the entrance of the next process can be prevented. Or it can prevent stagnation.

Note that it is more effective and preferable to make the downstream end of the tapered pipe protrude into the next process equipment such as a distillation column, since this is more effective in preventing backflow or stagnation of the gaseous catalytic cracking products.

As shown in Examples and Comparative Examples below, according to the method of the present invention, gaseous catalytic cracking products of heavy oil can be transferred without coking, and therefore the cracking reactor can be operated continuously for a long time. be able to.

Examples 1 to 8 and Comparative Examples When the gaseous decomposition products obtained by fluid catalytic cracking of kraate crude vacuum residue at a reaction temperature of 500°C using a nickel oxide ore catalyst are transferred from the reactor to the distillation column, Table 1 shows the number of days of continuous operation of the decomposition reactor when conditions such as temperature, gas flow rate in the transfer pipe, cross-sectional area of the transfer pipe, and shape of the downstream part of the transfer pipe are changed.

The shape of the tapered tube is as shown in Figure 2.
In addition, an electric heater was used to heat the transfer tube.

[Brief explanation of drawings]

Figure 1 is a diagram showing the gas flow state in the downstream cross section when the downstream part of the transfer pipe is a straight pipe, and Figure 2 is a diagram showing the gas flow state in the downstream cross section when the downstream part of the transfer pipe is a tapered pipe. It is a drawing showing the flow. 1...Transfer pipe, 2...Downstream part of transfer pipe,
3...Next process equipment (e.g. distillation column), α...
...Aperture angle.

Claims (1)

[Claims] 1 The temperature of the pipe wall of the transfer pipe for gaseous catalytic cracking products produced by decomposition of heavy oil is maintained at 540°C to 630°C, and the flow rate in the pipe for transferring the gaseous catalytic products is 45 m/s.
A method for transferring gaseous catalytic cracking products of heavy oil, characterized in that the gaseous catalytic cracking products of heavy oil are maintained at or above.