JPS61215693A - Multiple-purpose thermal decomposition system - Google Patents

Abstract

PURPOSE:To obtain an economically advantageous and effective thermal decomposition system capable of coping with different raw materials, by providing a second quencher with a plurality of process gas passages which are different in heat exchanging point so that the passages are switched over according to the use of different raw materials. CONSTITUTION:A process gas from a thermal decomposition oven is introduced into a center tube 11 through a sleeve 12 in such a manner that the process gas is not passed through a heat transferring tube 8. The heat transferring tube 8 and the center tube 11 are different in heat exchange capacity because of their remarkable difference in surface area which contributes to the heat transfer. Therefore, when the center tube 11 is used, the amount of heat exchange is easily controlled as compared with the case where the heat transferring tube 8 is used, which enables the adjustment of heat exchange to the raw material used. The amount of heat exchange in the tube 11 may also be adjusted by changing the length of the sleeve 12 at the portion inserted into the center tube 11 from L to L', which contributes to the attainment of a proper temp. of the process gas at the outlet of the second quencher.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multi-purpose pyrolysis system, and more particularly,
Different types of raw materials with hydrocarbon content are processed in the same pyrolysis furnace, quencher (
This relates to a system that enables thermal decomposition and rapid cooling heat exchange using a rapid cooling device.

[Conventional technology and problems to be solved]

In pyrolysis equipment that produces olefin fractions such as ethylene using hydrocarbons as raw materials, there is a pyrolysis furnace that pyrolyzes the raw material into predetermined desired components, and a pyrolysis furnace that cools the desired components produced by the reaction in a short time. and a quenching device to minimize secondary reactions to undesirable components. This quenching device is also required to perform the additional role of maximizing heat recovery.

Hydrocarbon feedstocks used in such pyrolysis equipment pressures generally range from relatively light specific gravity such as ethane and propane to relatively heavy specific gravity such as naphtha and gas oil. . It would be most desirable if these various raw materials could be processed using the same equipment as much as possible, but since each raw material requires different factors in terms of reaction, it must be said that this is not possible in reality.
When raw materials change, we respond by modifying or reworking some of our equipment. For example, the case where naphtha and gas oil are used as raw materials will be explained as follows.

These are petroleum fractions consisting of a mixture of various hydrocarbons, but in the case of naphtha, the boiling point under normal pressure is 50°C to 200°C.
In the case of gas oil, the temperature varies from about 150°C to 350°C. That is, gas oil contains more high-boiling fractions than naphtha; in other words, it condenses and becomes liquid at a higher temperature than naphtha. On the other hand, although the purpose of the quenching device in the above-mentioned pyrolysis equipment is to perform quenching and maximize heat recovery,
If the temperature falls below the above-mentioned condensation temperature, problems such as condensation and clogging may occur due to adhesion of condensate within the equipment and piping. This is a situation that must be avoided when feeding. Therefore, in commonly used pyrolysis equipment, the cooling temperature in the quenching device is approximately 350°C for naphtha and approximately 450°C for gas oil. This is determined based on the detailed properties of the raw materials, and if the types of raw materials differ, the equipment must be modified accordingly.

By the way, it is possible to consider processing both naphtha and gas oil as raw materials in one pyrolysis facility.
c) There is a conventional technique that has been proposed, which is shown in FIG.

The raw material is continuously supplied to the pyrolysis furnace 21, and the process gas that has undergone a predetermined reaction in the reaction coil 22 built into the pyrolysis furnace 21 is introduced into the primary quencher 23. The primary quencher 23 has a double-tube structure, and in the process of passing through the inner tube, the process gas is cooled by exchanging heat with high-pressure water filling the spaces between the inner and outer tubes. Part of this primary high pressure water is evaporated and introduced into the steam drum 31 via the riser pipe 28.
It also returns to the primary quencher 23 through the downcomer pipe 27, forming a circulation path.

The process gas cooled to a predetermined temperature by the primary quencher 23 is introduced into the secondary quencher 25 via the communication pipe 24 . This secondary quencher 25 usually employs a shell-and-tube system called a multi-tube system. The process gas passes through a large number of relatively small-diameter tubes, exchanges heat with high-pressure water on the shell side, is cooled to a predetermined temperature, and is then led out to the outlet pipe 26. On the other hand, the high-pressure water that has partially evaporated within the shell is introduced into the steam drum 31 via the riser pipe 30 and returns into the shell via the downcomer pipe 29, forming a circulation path.

Note that a plurality of primary quenchers 23 may be arranged in parallel, and in this case, they are collected into one in a collecting pipe in the middle of the communication pipe 24.

When the raw material is naphtha, the operation is performed according to the flow described above.

When the raw material is changed to gas oil, the process gas cooled to a predetermined temperature by the primary quencher 23 is separated in the middle of the communication pipe 24, and after being connected to the switching spool 32,
It is led out to the outlet pipe 26 via the bypass pipe 33.

That is, this is a method of adjusting the cooling temperature of the process gas by bypassing the secondary quencher 25.

To explain this diagrammatically in Figure 5, when the raw material is only gas oil, the primary quencher cools the process gas temperature from To to T1, and the secondary quencher cools the process gas temperature to T2. .

Generally, To is 800℃ to 850℃, T1 is 550 to 6
50°C, T2 is about 450°C. On the other hand, when the raw material is only naphtha, heat is recovered up to T3 in the secondary quencher. Generally, T3 is about 350'C. If naphtha and gas oil are used as raw materials, the switching method described above will be used, but after considering the amount of heat recovery and the size of the quencher, the cooling temperature in the primary quencher should be set to Tl.
and T2, and when using gas oil, bypass the secondary quencher and lead it to the subsequent equipment, and when using naphtha, lead it to the subsequent equipment through the secondary quencher. Become.

Although it is possible to operate a pyrolysis system having such a configuration (FIGS. 4 and 5) using different raw materials of naphtha and gas oil, the above-mentioned problems occur.

That is, as described above, the quencher constitutes a boiler that generates high-pressure steam as the process gas is cooled. Therefore, if the secondary quencher is bypassed when the raw material is gas oil, the quencher will not be able to exchange heat, and the steam drum 31, riser pipe 30. Downcomer pipes 29 and 2
Next, high-pressure boiler water is no longer circulated in the quencher shell, and the quencher shell is always filled with high-pressure water. the result,
In particular, high pressure water stagnates inside the shell of the secondary quencher 25,
Contamination due to the accumulation of impurities in high-pressure water over a long period of time leads to corrosion such as pitting, and the temperature of the high-pressure water decreases due to heat dissipation from the shell surface, reducing the amount of steam generated. Therefore, constant attention must be paid to maintenance without using a secondary quencher that has multiple complex seal structures.

In addition, the communication pipe 24 is usually a large diameter pipe with a diameter of 300 to 600 nm, but in order to absorb the thermal expansion of the pipe without difficulty, the switching pipe 33 needs to have a very tight loop shape. The actual work is not easy, as the amount of material increases and the switching operation becomes a large task.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and
By making it possible to appropriately adjust the heat recovery amount of the process gas without bypassing the quencher, we provide an economical and efficient multipurpose pyrolysis system that can handle different raw materials. be.

[Means for solving problems]

The present invention provides, in the above pyrolysis system, a plurality of process gas passages having different amounts of heat exchange in the secondary quencher. In the case of any raw material use, the secondary quencha can be used at all times according to the original purpose, and can be operated without switching to the pie -pass line. The invention will be explained in detail based on illustrated embodiments.

FIG. 1 shows a secondary quencher in a multi-purpose pyrolysis system according to one embodiment of the present invention.

The shell 1 is connected to an inlet channel 2 via an inlet tube plate 3;
They are also respectively connected to outlet channels 5 via outlet tube plates 4 . Each of the heat exchanger tubes 8 is arranged between the inlet tube sheet 3 and the outlet tube sheet.

When using this configuration, the process gas introduced from the inlet nozzle 6 passes through the inlet channel 2, enters the heat exchanger tube 8, exchanges heat with high-pressure water filled in the shell 1, and generates steam. to occur. The generated steam is guided through a riser pipe 9 to a separate steam drum (see FIG. 4), and from the drum, high-pressure water is replenished into the shell 1 via a downcomer pipe 10.

In the present invention, the center tube 11 is arranged along the longitudinal center axis of the secondary quencher having the above structure. The center tube 11 usually has a sufficiently larger diameter than the heat exchanger tube 8. A sleeve 12 is installed in the inlet channel 2, and one end of the sleeve 12 is connected to the inlet nozzle 6.
The other end is inserted into the center tube 11,
The distal end portion has an expanded shape and is configured to be able to come into close contact with the inner wall of the center tube 11 (FIG. 2). A seal cover 13 is removably provided on each channel side of the inlet tube plate 3 and the outlet tube plate 4 so as to cover the heat exchanger tubes 8.

[Effect]

Next, a method of using the secondary quencher having the above configuration will be explained.

As mentioned above, when the raw material is gas oil, the cooling temperature of the process gas produced by thermally decomposing it must be relatively high.

Therefore, conventionally, as shown in FIG. 4, the process gas supplied from the primary quencher bypassed the secondary quencher. In this regard, in the present invention, the process gas is introduced into the secondary quencher, and is first introduced into the center tube 11 via the sleeve 12, but at that time, it is prevented from passing through the heat exchanger tube 8. The heat exchanger tube 8 and the center tube 11 have significantly different surface areas that contribute to heat conduction, as shown in FIG. 1(b), and therefore have different amounts of heat exchange. Therefore, compared to the case where the heat exchanger tube 8 is used, when the center tube 11 is used, the amount of heat exchange can be suppressed, and the amount of heat exchange can be adjusted to match the raw material used.

In this case, as shown in FIG. 2, the amount of heat exchange within the center tube 11 can also be adjusted by changing the insertion length of the sleeve 12 into the center tube 11 from L to L'. A suitable process gas temperature at the encher outlet can then be obtained.

Next, a case where the raw material is changed from gas oil to naphtha will be explained. As mentioned above, naphtha is cooled so that the process gas temperature is relatively lower than when using gas oil. To do this, remove the sleeve 12 and seal cover 13, and attach the center tube cover 14 to the center tube 11 as shown in FIG. Amount of heat exchange can be obtained.

In the illustrated embodiment, one center tube is installed in the secondary quencher, but a plurality of center tubes may be installed, and they do not necessarily need to be placed on the central axis, but may be installed on the outer periphery of the tube sheet. A similar effect can be obtained.

Furthermore, when the flow of the process gas generated by thermal decomposition is disturbed or it stagnates, a phenomenon of carbonization (so-called coking) occurs. It is also effective to constantly purge.

〔Effect of the invention〕

As described above, the present invention can be applied even when different cooling temperatures of the process gas are required in a pyrolysis system that uses different types of raw materials together, and therefore it is possible to use a switching spool and a bypass instead of the conventional one. Moreover, by constantly using a quencher, it can be operated as a boiler system and troubles can be prevented, which has great effects such as economical efficiency and system simplification.

[Brief explanation of the drawing]

1 to 3 are diagrams showing a secondary quencher of a multipurpose pyrolysis system according to an embodiment of the present invention, in which FIG. 1(a) is a vertical cross-sectional view of the secondary quencher, and FIG. A-A cross-sectional view of (A), Figure 2 is a partially enlarged vertical cross-sectional view of Figure 1), Figure 3 is a vertical cross-section showing another example of the use of the secondary quencher shown in Figure @1. 4 is a schematic explanatory diagram of a conventional pyrolysis system, and FIG. 5 is a diagram showing an example of use of the system of FIG. 4. DESCRIPTION OF SYMBOLS 1... Shell, 2... Inlet channel, 3... Inlet tube sheet, 4... Outlet tube sheet, 5... Outlet channel,
6... Inlet nozzle, 7... Outlet nozzle, 8... Heat exchanger tube, 9... Rising pipe, 10... Downcomer pipe, 11...
Center tube, 12... Sleeve, 13... Seal cover, 14... Center tube cover.

Claims (3)

[Claims] (1) In a multipurpose pyrolysis system that includes a pyrolysis furnace, a primary quencher, and a secondary quencher, and performs rapid cooling heat exchange after pyrolysis of different materials, the secondary quencher is provided with a plurality of process gas passages with different amounts of heat exchange. A multi-purpose pyrolysis system characterized in that the process gas passage is configured to be switchable according to the use of different raw materials. (2) The process gas passage consists of a relatively large-diameter center tube and a small-diameter heat exchanger tube, and the center tube is removably provided with a length-adjustable tube, and the heat exchanger tube is provided with a removable inlet tube plate. A multi-purpose pyrolysis system according to claim 1, comprising: (3) The multipurpose pyrolysis system according to claim 1 or 2, wherein the process gas passage has an inlet channel portion for preventing coking of the process gas.