JPH0315539Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a hydrocarbon pyrolysis device, and particularly to a pyrolysis device for producing olefins such as ethylene and propylene by pyrolyzing hydrocarbons such as naphtha. Regarding.

[Background of the idea]

When producing olefins such as ethylene and propylene by thermally decomposing hydrocarbons such as naphtha,
It is desired to increase the yield of ethylene as high as possible and to minimize the decrease in the yield of propylene. For this reason, in order to particularly improve the yield of ethylene, the reaction temperature in the pyrolysis furnace should be raised, the hydrocarbon partial pressure in the reaction tube should be lowered, and the residence time of the cracked gas should be shortened. development is underway.

In a hydrocarbon pyrolysis furnace, the cracked gas is heated to a predetermined temperature in a reaction coil and pyrolyzed.
In order to freeze over-decomposition and secondary reactions of cracked gas,
It must be led to a subsequent quench heat exchanger and quenched as quickly as possible. FIG. 7 shows this process. As shown in Figure 7, the functions of the cracking furnace reaction coil and the quenching heat exchanger are completely opposite, so even if the cracking furnace reaction coil is improved, its structural limitations will make it difficult to match the cracking furnace reaction coil. An insulated high-temperature piping section is required to connect to the cold heat exchanger.

FIGS. 5 and 6 show an example of a conventional pyrolysis furnace having an insulated high-temperature piping section as described above. In FIG. 5, a plurality of reaction tubes 3 installed in a combustion chamber 1 of a cracking furnace equipped with a burner 2 are assembled, and cracked gas is fed into multiple tubes through a high-temperature pipe 5 provided with a heat insulating layer 4 on the outer circumferential surface. It is designed to lead to a quenching heat exchanger 6 of the formula. In FIG. 6, the outlet portions of a plurality of reaction tubes 3 are extended as they are, and the decomposed gas is passed through a plurality of high-temperature pipes 5 provided with a heat insulating layer 4 on the outer circumferential surface to a plurality of double-pipe quenching tubes. Exchanger 7
and then to a heat exchanger 8.

However, in such a conventional pyrolysis furnace, over-decomposition and secondary reactions of the decomposed gas proceed in the portion of the high-temperature pipe 5 where the heat-insulating layer 4 is provided, that is, in the heat-insulating region. As a result, depending on the decomposition conditions of the reaction coil and raw material gas, the cracked gas leaving the reaction coil passes through the above-mentioned adiabatic region and the quenching heat exchanger and is cooled to a temperature at which over-decomposition stops. As shown in Figure 7, the yield of ethylene is 1~
Although the amount increases by 2%, the yield of propylene drops significantly to 3 to 5%, and the yield of methane and hydrogen gas, which have low added value, increases.

On the other hand, if instead of providing a heat insulating area to freeze over-decomposition and secondary reactions of cracked gas, the portion corresponding to the high-temperature piping is housed in a combustion chamber equipped with a general burner, the following problems arise. That is, the high-temperature piping shown in Figure 5 has a diameter of about 8 to 12 inches, and the high-temperature piping shown in Figure 6 generally has a diameter of about 4 to 6 inches, which is smaller than the reaction tube size in the pyrolysis furnace. This results in a large diameter. If such a large-diameter, high-temperature piping section that maintains a high decomposition reaction temperature (approximately 860°C) is housed in a combustion chamber with a general burner, the heat transfer effect will be poor and local overheating will occur. This may cause caulking, material deterioration,
On the other hand, if a large combustion chamber is used to avoid this problem, it will be difficult to connect the reaction tubes and the quenching heat exchanger. Currently, the high temperature piping section has a heat insulating layer.

[Purpose of invention]

An object of the present invention is to provide a hydrocarbon pyrolysis apparatus that eliminates the drawbacks of the prior art described above and can reduce the decrease in propylene yield while maintaining a high ethylene yield.

[Summary of the idea]

In this invention, a catalytic combustion device is installed in the piping connecting the reaction tube and the quenching heat exchanger in the pyrolysis furnace, and this piping is used as a reaction tube that can control the required reaction temperature. By connecting directly to the exchange, the above objectives are solved at once.

[Example of idea]

Embodiments of the present invention will be described below based on the accompanying drawings.

1 and 2 respectively show an embodiment of the present invention. In FIG. 1, a reaction tube 3 in a cracking furnace combustion chamber 1 is connected to a quenching heat exchanger 6 via a high temperature pipe 9. A smoke pipe 10 is attached to the outer periphery of the pipe. A heat-resistant expansion joint 11 is provided at the connection between the smoke pipe 10 and the cracking furnace combustion chamber 1, and a fuel gas nozzle 12 and an air nozzle 13 are attached to the smoke pipe 10 at a position close to the quenching heat exchanger 6. . In the figure, reference numeral 14 denotes a combustion catalyst packed bed, which is provided in an annular shape in the smoke pipe 10, and a heat insulating layer 15 is provided around the outside of the smoke pipe 10.

In such a hydrocarbon pyrolysis furnace, cracked gas from the reaction tube 3 is introduced into the quenching heat exchanger 6 via the high temperature pipe 9. At this time, part of the fuel gas supplied to the burner 2 installed in the combustion chamber 1 of the cracking furnace is introduced from the fuel gas nozzle 12, and combustion air is introduced from the air nozzle 13. The ratio of combustion air and fuel gas is controlled, and the mixed gas is introduced into the combustion catalyst packed bed 14, where the fuel gas is combusted. This combustion gas flows through the smoke pipe 10 and exchanges heat with the cracked gas in the high-temperature piping section 9, and is led to the cracking furnace combustion chamber 1 via the expansion joint 11, where the heat is recovered for preheating the raw material gas.

The difference between the apparatus shown in FIG. 2 and the apparatus shown in FIG. 1 is that in the apparatus shown in FIG. In the apparatus shown in the figure, each reaction tube 3 in the cracking furnace combustion chamber 1 is extended to form each high-temperature pipe 9,
Each high-temperature pipe 9 is provided with a heating area by a combustion catalyst similar to that shown in FIG. Therefore, in FIG. 2, members corresponding to those shown in FIG. 1 are designated by the same reference numerals.

In the apparatus shown in FIG. 2, the operation shown in FIG. 1 is performed for each high-temperature pipe 9.

In the equipment shown in Figures 1 and 2, the high-temperature piping section can be used to function as a reaction tube, can be directly connected to a quenching heat exchanger, and uses a heating method using a combustion catalyst. Therefore, the heating combustion gas undergoes a combustion reaction in a short time, and the combustion temperature can be controlled to a predetermined reaction temperature level by controlling the air-combustion ratio. Therefore, the temperature of the cracked gas near the outlet of the high-temperature pipe 9 can be easily and accurately controlled to the temperature required for the reaction, so as shown in Figure 4, the ethylene yield can be maintained high and the decrease in the propylene yield can be minimized. In addition, coking of cracked gas can be avoided, and the conventional insulated piping can be omitted and the high-temperature piping can be used as a reaction tube, making the equipment more compact.Moreover, the reaction tube in the combustion chamber of the cracking furnace can be shortened. It is possible to do this.

Incidentally, when heating the high-temperature piping section by gas generated from the combustion chamber of the decomposition furnace, the decomposition reaction temperature is approximately 860°C.
In order to maintain the exhaust gas temperature at a high temperature of °C and prevent local heating of large-diameter pipes with poor heat transfer effects, an extremely limited exhaust gas temperature level is required. It becomes necessary.

[Effect of idea]

As described above, according to the hydrocarbon pyrolysis apparatus of the present invention, the decrease in propylene yield can be minimized while maintaining a high ethylene yield without causing coking of cracked gas with a compact apparatus. be able to.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing one embodiment of the hydrocarbon pyrolysis apparatus according to the present invention, and FIG. 2 is a schematic block diagram showing another embodiment of the hydrocarbon pyrolysis apparatus according to the present invention. , Fig. 3 is a cross-sectional view taken along line A-A in Fig. 1, and Fig. 4 shows the temperature of the cracked gas according to the flow direction (residence time) of the cracked gas in the apparatus shown in Figs. 1 and 2. , a graph showing the change process of the yield of ethylene and propylene, Figures 5 and 6 are schematic diagrams showing the conventional hydrocarbon thermal decomposition equipment, respectively, and Figure 7 is a graph showing the change process of the yield of ethylene and propylene. 1 is a graph showing the change process of the temperature of cracked gas and the yield of ethylene and propylene according to the flow direction (residence time) of cracked gas. 1... Cracking furnace combustion chamber, 2... Burner, 3... Reaction tube, 4, 15... Heat insulation layer, 5, 9... High temperature piping, 6, 7... Rapid cooling heat exchanger, 8... Heat Exchanger, 10... Smoke pipe, 11... Expansion joint, 12...
Fuel gas nozzle, 13... Air nozzle, 14...
Combustion catalyst packed bed.

Claims (1)

[Claims for Utility Model Registration] (1) A catalytic combustion device is installed in a high-temperature piping section that connects a reaction tube in a hydrocarbon pyrolysis furnace and a heat exchanger for rapidly cooling the cracked gas in the reaction tube. A hydrocarbon pyrolysis device characterized by having been installed. (2) The catalytic combustion device includes a combustion catalyst layer filled in a smoke pipe provided around the outer periphery of the high-temperature piping section and close to the heat exchanger; The hydrocarbon pyrolysis apparatus according to claim 1, which comprises a fuel gas nozzle and an air nozzle, which are provided between a cracked gas inlet of a heat exchanger and a cracked gas inlet of a heat exchanger.