JPH04257692A - Heat exchanger for thermal decomposition furnace - Google Patents

Abstract

PURPOSE:To enable sensitive heat held by generated gas to be recovered under a high efficiency by a method wherein a plurality of cooling pipes are branched and connected in parallel with a single cooling pipe and two cooling portions having generated gas outlets of the plurality of cooling pipes are disposed within the same shell having heat exchanging medium flowed therein. CONSTITUTION:Generated gas of high temperature produced from a thermal cracking furnace for hydro-carbon keeps its high speed flow at a part of a primary cooling pipe 31 and is cooled to a temperature less than a freezing temperature of secondary reaction. The gas is changed into a low speed flow at a part of a branched secondary cooling pipe 32 and at the same time a cooling area is increased. Due to this fact, an entire length of the cooling device is shortened more than that of the double-piped structure in which the prior art primary cooling device and the secondary cooling device are integrally formed together and so an intermediate communication pipe between the high temperature cooling pipe connected to a reaction pipe of the thermal cracking furnace and the prior art primary and secondary cooling devices can be eliminated. Accordingly, a pressure loss caused by a pipe resistance of the produced gas can be substantially reduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a heat exchange device for rapid cooling used in a hydrocarbon pyrolysis furnace, and in particular rapidly cools high-temperature pyrolysis gas such as olefinic hydrocarbons to freeze secondary reactions. The present invention relates to a heat exchange device having a structure suitable for recovering sensible heat.

0002

[Prior Art] Conventionally, pyrolysis furnaces use liquid hydrocarbons such as naphtha (crude gasoline), kerosene, and light oil as raw materials and thermally decompose them to produce olefin hydrocarbons such as ethylene and propylene. A two-stage cooler (quencher) is used to freeze the secondary reaction of high-temperature pyrolysis gas and recover sensible heat. FIG. 3 shows a conventional hydrocarbon pyrolysis system using this two-stage cooler. The structure of the primary cooler used in the hydrocarbon pyrolysis system shown in Figure 3 is shown in Figure 4.
The structure of the secondary cooler is shown in Figure 5.

In FIG. 3, the pyrolysis furnace 1 includes a burner 2.
The burner 2 heats and decomposes the raw material hydrocarbon flowing through the reaction tube 3. The decomposed product gas is introduced into the primary cooler 5 via the high temperature communication pipe 4. The primary cooler 5 has the main purpose of freezing the secondary reaction of the high-temperature product gas, and cools the high-temperature product gas at high speed to the reaction freezing temperature using cooling water supplied from the downcomer pipe 11 of the primary cooler. cooled down. The generated gas cooled to a predetermined temperature in the primary cooler 5 is collected at the outlet header 6 of the primary cooler 5, and sent to the secondary cooler 8 via an intermediate connecting pipe 7, where it is cooled to a predetermined temperature. In the cooler 8, the generated gas exchanges heat with the cooling water supplied from the downcomer pipe 12 of the secondary cooler, recovers sensible heat, and is cooled. Rising pipes 9, 10 and downcomer pipes 11, 1 are provided for both the primary cooler 5 and the secondary cooler 8, respectively.
The heat is exchanged with high-pressure water supplied into the steam drum 13, and the heat is recovered as high-pressure steam from the steam drum 13.

As shown in FIG. 4, the primary cooler 5 has an outer tube 1.
4 and an inner pipe 15, the produced gas inlet part 16 of the primary cooler 5, the produced gas outlet part 17 of the primary cooler 5, the downcomer pipe connection nozzle 18, and the riser pipe connection. Nozzle 1
9. FIG. 5 shows the structure of the secondary cooler 8, which is a shell-and-tube type heat exchanger. It is equipped with an outlet section 22, a downcomer pipe connection nozzle 18, and a riser pipe connection nozzle 19. Secondary cooler 8
The produced gas inlet section 21 and the produced gas outlet section 22 of the secondary cooler 8 are filled with a heat insulating material 23 . Generally, in order to cool the produced gas at high speed by the primary cooler 5 to the secondary reaction freezing temperature of 600 to 700°C,
The mass velocity of the generated gas in the secondary cooler 5 is set to 60 to 120 kg.
/m2・s, and the secondary cooler 8 has a high mass velocity of 30 to 60 kg/m2・s in order to suppress the condensation of high boiling point components.
A low mass velocity of s is assumed. Therefore, as shown in FIGS. 4 and 5, the inner pipes 15 of the primary cooler 5 and the cooling pipes 25 of the secondary cooler 8 have different diameters, and .

As an example of this type of heat exchanger, a double tube type heat exchanger for cooling cracked gas has been proposed, for example, in Japanese Patent Publication No. 53-44251.

[0006]

[Problems to be Solved by the Invention] As mentioned above, the conventional two-stage heat exchange device has an excellent function of freezing the side reactions of the high-temperature gas produced by thermal decomposition and suppressing the generation of coke. Although it has the advantage of increasing the operating time of the pyrolysis furnace, it has the disadvantage that the heat exchange device has a complicated structure because the primary and secondary coolers are separated and installed separately. .

Furthermore, since the piping system has many bends, such as the high-temperature connecting pipe between the reaction tube and the primary cooler of the pyrolysis furnace and the intermediate connecting pipe between the primary and secondary coolers, the pyrolysis products are There was a problem in that the pressure loss in the gas system increased. As shown in Figures 6 and 7, this increase in pressure drop not only reduces the yield of olefin hydrocarbons, but also promotes the formation of coke in the high temperature section of the heat exchanger, increasing the operating time of the pyrolysis furnace. The problem was that it became shorter.

An object of the present invention is to solve the above-mentioned problems in the prior art, and to solve the above-mentioned problems in the prior art, and to solve the conventional two-dimensional problem, which involves increasing the mass velocity of the pyrolysis product gas in the high-temperature part and rapidly cooling it to freeze the secondary reaction. A heat exchanger for pyrolysis furnaces that can recover the sensible heat possessed by the produced gas with high efficiency without impairing the function of the stage heat exchanger, has a simple structure with low pressure loss, and has low equipment costs. The goal is to provide equipment.

[0009]

[Means for Solving the Problems] In order to achieve the above object of the present invention, in a heat exchange device for rapidly cooling high temperature pyrolysis product gas in a hydrocarbon pyrolysis furnace, a secondary reaction freezing of the product gas is provided. For one primary cooling pipe whose main purpose is to recover the sensible heat of the produced gas, two or three or more secondary cooling pipes are connected in parallel to This makes it possible to control the mass velocity of the generated gas flowing in the cooling pipe to an optimal value that meets each of the above objectives.

Specifically, the heat exchange device of the present invention includes a primary cooling section consisting of one cooling pipe, and a plurality of cooling pipes of two or more using Y-shaped bend pipes or three-pronged bend pipes. The generated gas outlet portions of the plurality of branched cooling pipes are connected in parallel and gathered at one place using the above-mentioned bend pipe, etc., and the plurality of cooling pipes are connected in an elliptical loop structure.
The structure constitutes a secondary cooling section, and the primary cooling section and the secondary cooling section are integrally disposed within the same shell (outer tube) through which a heat exchange medium such as boiler water flows.

[0011] A downcomer header, a riser header, etc. are provided at both ends of the shell, an inlet connection section for high temperature pyrolysis product gas is provided in the primary cooling section, and an inlet connection section for the high temperature pyrolysis gas is provided in the secondary cooling section. is achieved by providing an outlet connection for the product gas.

[0012] The present invention provides a primary cooling section that rapidly cools high-temperature product gas generated from a pyrolysis furnace for producing olefinic hydrocarbons inside a cooling pipe to freeze the secondary reaction, and a primary cooling section that freezes the secondary reaction. In a heat exchange device equipped with a secondary cooling section that recovers sensible heat held by gas, the heat exchange device includes a primary cooling section consisting of a single cooling pipe, and a secondary cooling section consisting of a single cooling pipe.
The heat exchange medium flows through the secondary cooling section, which has a structure in which a plurality of cooling pipes are branched and connected in parallel, and the generated gas outlet parts of the plurality of branched cooling pipes are gathered and connected in one place. They are arranged integrally within the same shell.

[0013] Furthermore, in the heat exchange device of the present invention, the primary cooling section and the secondary cooling section may be connected by a U-shaped bent pipe and disposed integrally within the U-shaped shell. is also possible.

[0014]

[Operation] According to the heat exchange device of the present invention, the high-temperature product gas generated from the hydrocarbon pyrolysis furnace maintains a high flow rate (high mass velocity) in the primary cooling pipe section, while undergoing the secondary reaction. In the section of the secondary cooling pipe that is cooled below the freezing temperature and branched off, the flow rate changes to a low flow rate (low mass velocity), and at the same time the cooling (
Heat exchange) area can be increased, so compared to the conventional 1
The overall length of the cooler is shorter than that of a double-tube structure in which the primary and secondary coolers are integrated, and the high-temperature communication pipe connected to the reaction tube of the pyrolysis furnace and the conventional Since the intermediate communication pipe between the primary and secondary coolers can be omitted, pressure loss due to pipe resistance of the generated gas can be significantly reduced. In addition, since multiple secondary cooling pipes are connected in parallel to form a loop structure, the length of the heat exchanger as a whole can be shortened, and at the same time, the shell (outer pipe)
It can absorb the difference in thermal expansion between the inner pipe and the cooling pipe (inner pipe),
It becomes possible to significantly reduce damage to the heat exchanger due to thermal stress.

[0015]

[Embodiment] An embodiment of the present invention will be described below in more detail with reference to the drawings. FIG. 1 shows an example of the configuration of a heat exchange device for a pyrolysis furnace according to the present invention. In the figure, the overall structure of the heat exchanger is a so-called double-structured heat exchange device consisting of an outer pipe (shell) 30, which is a shell or pipe, and inner pipes, which are a primary cooling pipe 31 and a secondary cooling pipe 32. However, one primary cooling pipe 31 and two, three, or more secondary cooling pipes 32 are provided in one outer pipe 30, and Y is provided at both ends of the secondary cooling pipe 32. Type bend or three-pronged bend 3
The feature is that branch pipes such as 3 and 34 are provided for the secondary cooling pipe 32. Further, one end of the primary cooling pipe 31 is butt welded to a downcomer pipe header 35, and the other end is welded to a three-pronged bend 33.
Butt welded with etc.

Both ends of the secondary cooling pipe 32 are connected to a three-pronged bend 3.
3 and 34, and the other end of the three-pronged bend 34 is butt welded to a riser header 36. Downpipe header 3
5 is provided with a downcomer pipe connection nozzle 37, and the riser pipe header 36 is provided with a riser pipe connection nozzle 38, and the riser pipe and downcomer pipe of the boiler system are connected to these connection nozzles 37 and 38, respectively. be done. Further, a generated gas inlet nozzle 39 is provided at one end of the primary cooling pipe 31, and is lined with a heat insulating material 40. At one end of the secondary cooling pipe 32,
A product gas outlet nozzle 41 is provided. Further, it is preferable that the riser pipe header 36 and the outer pipe 30 and the outer pipe 30 and the downcomer pipe header 35 have a butt welded structure. In other words, all of the main parts of the container containing the high-pressure boiler water are butt-welded, and one of the structural features is that the strength of the welded structure is improved.

Next, the operation of the heat exchange device exemplified in this embodiment will be explained. High-temperature product gas decomposed in the pyrolysis furnace 1 shown in FIG. 3 is introduced from the reaction tube 3 to the product gas inlet nozzle 39 shown in FIG. 1, and first introduced into the primary cooling pipe 31. The produced gas introduced into the primary cooling pipe 31 is rapidly cooled by exchanging heat with the boiler water supplied from the downcomer connection nozzle 37, and is rapidly cooled to below the freezing temperature of the secondary reaction, and is then formed into a three-pronged bend (branched It is led to the secondary cooling pipe 32 via the pipe 33. The produced gas guided to the secondary cooling pipe 32 is divided into two or three or more systems, and the produced gas is cooled by further heat exchange with the boiler water that was heat exchanged in the primary cooling pipe 31. The produced gas is sent to the next process from the outlet nozzle 41. Boiler water that has received heat is
Part of the steam becomes high-pressure steam and is guided to the steam drum 13 shown in FIG. 3 via the riser header 36 and the riser connection nozzle 38. In this example, one tube (1
In order to prevent an increase in the pressure loss of the generated gas due to high flow rate, the secondary cooling pipe 32 is
Alternatively, there may be three (two or three lines), and the flow rate of the generated gas in the secondary cooling pipe 32, that is, the mass velocity, can be freely selected according to the raw material properties. In addition, the reaction tube 3 and the generated gas inlet nozzle 39 can be directly connected, which is different from the conventional one.
Since the high-temperature communication pipe 4 and the intermediate communication pipe 7 that connect to the secondary coolers 5 and 8 can be omitted, it is possible to minimize the pressure loss in the heat exchange device, and the conventional two-stage cooling The system also has advantages. In addition, since the generated gas is guided to the heat exchange device at high temperature, the internally installed primary cooling pipe 31 and secondary cooling pipe 32,
A difference in thermal expansion occurs between the outer tube 30 and the secondary cooling tube 32, which has a loop structure with Y-shaped bends or three-pronged bends 33, 34, etc., in order to absorb this difference in thermal expansion. All of these have a structure that allows for butt welding, and has a structure that further improves welding strength.

FIG. 2 shows another embodiment of the present invention, in which a primary cooling pipe 31 and a three-pronged bend (branch pipe) 33 are shown.
A 180 degree bend 42 is installed in between. 1
The welded part between the secondary cooling pipe 31 and the downcomer pipe header 35, and
As shown in FIG. 2, thermal expansion can freely occur in the upper part of the figure, starting from the weld between the three-pronged bend (branch pipe) 34 at the outlet of the generated gas of the secondary cooling pipe 32 and the precipitation header 35, as shown in FIG. , When the cooling temperature level of the generated gas is high or is likely to rise, such as the gas produced by thermal decomposition of heavy feedstock hydrocarbons, the primary cooling pipe 31 and the secondary cooling pipe 32 and the external This is particularly effective because the temperature difference between the pipe 30 and the resulting difference in thermal expansion becomes large.

[0019]

[Effects of the Invention] As explained in detail above, according to the heat exchange device for a pyrolysis furnace of the present invention, a single primary cooling pipe and two
~ By combining three or more secondary cooling pipes, the flow velocity (mass velocity) of the generated gas in each cooling pipe can be increased.
can be changed to any set value, allowing for the contradictory effects of fast cooling aimed at freezing the secondary reaction of high-temperature product gas and slow cooling mainly aimed at recovering sensible heat and low pressure loss. This is a high-performance heat exchange device that can achieve both purposes with a single heat exchange unit. In addition, by omitting the connecting piping between the primary cooling pipe and the secondary cooling pipe and arranging the secondary cooling pipes in parallel (loop configuration), the pressure loss of the generated gas can be reduced and the thermal expansion difference between the inner and outer heat transfer pipes can be reduced. It has a structure that can absorb stress, and is a high-performance heat exchange device with a long decoking cycle and the advantages of an improved olefin hydrocarbon yield and a two-stage cooling system. Furthermore, since the heat exchange section is a simple combination of pipe elements, equipment costs can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the structure of a heat exchange device for a pyrolysis furnace exemplified in an embodiment of the present invention.

FIG. 2 is a sectional view showing an example of the structure of a heat exchange device for a pyrolysis furnace illustrated in an example of the present invention.

FIG. 3 is a flow diagram showing the configuration of a conventional pyrolysis furnace and heat exchange device.

FIG. 4 is a sectional view showing the structure of a conventional primary cooler.

FIG. 5 is a sectional view showing the structure of a conventional secondary cooler.

FIG. 6 is a graph showing the pressure loss in the heat exchange device exemplified in the example of the present invention in comparison with a conventional type.

FIG. 7 is a graph showing the yield of olefin hydrocarbons in the heat exchange device exemplified in the examples of the present invention in comparison with a conventional type.

[Explanation of symbols]

1...Pyrolysis furnace 2...Burner 3...Reaction tube 4...High temperature connecting pipe 5...Primary cooler 6...Exit header 7...Intermediate connecting pipe 8...Secondary cooler 9,10...Rising pipe 11, 12... Downpipe 13...Steam drum 14...Outer tube 15...Inner tube 16, 21...Produced gas inlet part 17, 22...Produced gas outlet section 18, 37... Downpipe connection nozzle 19, 38...Rising pipe connection nozzle 20...Thermal sleeve 23,40...insulation material 24...Shell 25...Cooling pipe 26...Boiler water inlet 27...Boiler water outlet 28...Produced gas inlet 29...Produced gas outlet 30...Outer tube (shell) 31...Primary cooling pipe 32...Secondary cooling pipe 33, 34...Three-pronged bend (branch pipe) 35... Downpipe header 36...Rising pipe header 39...Produced gas inlet nozzle 41...Produced gas outlet nozzle 42...180 degree bend

Claims (3)

[Claims] Claim 1: A primary cooling section that rapidly cools high-temperature product gas generated from a pyrolysis furnace for producing olefinic hydrocarbons inside a cooling pipe to freeze a secondary reaction; In a heat exchange device equipped with a secondary cooling section that recovers retained sensible heat, the heat exchange device has a primary cooling section consisting of a single cooling pipe, and two or more cooling pipes in the single cooling pipe. The secondary cooling section has a structure in which multiple cooling pipes are branched and connected in parallel, and the generated gas outlet parts of the branched cooling pipes are collected and connected in one place. A heat exchange device for a pyrolysis furnace, characterized by being integrally arranged within a shell. [Claim 2] In claim 1, the primary cooling section and the secondary cooling section are connected by a U-shaped bent pipe and are integrally arranged within a U-shaped shell. Features of heat exchange equipment for pyrolysis furnaces. 3. Claim 1 or claim 2, wherein the connection part between the primary cooling part and the secondary cooling part made up of a plurality of cooling pipes and the generated gas outlet part of the secondary cooling part made up of a plurality of cooling pipes are provided. A heat exchange device for a pyrolysis furnace, characterized in that a plurality of secondary cooling tube groups constituting a secondary cooling section are connected in a loop structure using Y-shaped bend pipes or three-pronged bend pipes.