JPH0649868B2 - Hydrocarbon pyrolysis furnace - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pyrolysis furnace for hydrocarbons, and more particularly to a pyrolysis furnace suitable for optimizing a pyrolysis reaction of a fluid in a pipe.

[Conventional technology]

In naphtha and other hydrocarbon pyrolysis furnaces, the main product, ethylene, as well as the propylene yield of by-products is improving, or the ratio of the two is changing. The shape of the coil has changed drastically.

For example, although FIGS. 12 and 13 show a conventional general structure, a radiant coil 3 is arranged on the longitudinal center of the furnace 2 of the decomposition furnace body 1. A large number of burners 4 are installed on the side surfaces on both sides of the coil, and various types of radiant coil shapes are installed as shown in FIG. 14 and used properly according to the purpose of use. Type 1 (Fig. 14 (a)) is the most orthodox coil shape, and based on this, type 2 (Fig. 14 (b)) and type 3 (Fig. 14 (c)) are becoming the mainstream these days. is there. These are called a merging method, in which the coil inlet side is composed of multiple passes, and the coil is merged and merged in the middle part to form one pass on the outlet side. Use a relatively small diameter pipe for the multi-pass part and a large diameter pipe after merging.
The flow velocity of the fluid in the pipe is set to be equal. For this purpose, as shown in FIG. 15, in the heat flux distribution along the length of the radiant coil in the furnace, the fluid temperature distribution in the coil is as shown in A of FIG. On the other hand, from the viewpoint of reaction in the coil, it is known that it is desirable to raise the fluid temperature as quickly as possible at the coil inlet portion, and therefore the direction B in FIG. 16 is directed. For this purpose, it is important to have a large amount of heat transfer capacity on the coil inlet side, and for that reason, by increasing the number of passes on the coil inlet side and reducing the diameter of the pipe, it is possible to increase the heat transfer amount, that is, the heat flux. This is what we are aiming for. Type 4 (Fig. 14 (d)) is a development of this theory to the utmost limit, which is called a straight type, which is a variant of tape 2 to type 3 for so-called high severity cracking.

[Problems to be solved by the invention]

By the way, in the thermal decomposition reaction of ethylene, the reaction is promoted by lowering the hydrocarbon partial pressure in the coil together with the above temperature distribution. Therefore, it is better to reduce the fluid pressure loss in the coil. However, as shown in Type 1 to Type 3, all have a hairpin structure having a 180 ° bend, and the pressure loss in this bend portion accounts for a large proportion. In this sense, a bend-free structure is desirable, and Type 4 is ideal. However, this cannot secure the length of the coil tube from the viewpoint of heat transfer. On the other hand, if you try to secure
The small-diameter pipes are arranged in multiple rows to give a very high level of heat flux, and the operation must be extremely severe.
There are also difficulties such as shortening the decoking period for small-diameter pipes, but the fact that they have been adopted in very few parts has not reached the mainstream.

An object of the present invention is to eliminate the drawbacks of the above-described conventional merged-type coil, to secure the amount of heat transfer required at the coil inlet side, and to eliminate the bend structure to reduce the pressure loss in the pipe, which is substantially conventional. It is possible to provide a pyrolysis furnace that enables the coil arrangement that could not be installed at the same time and reduces the coil installation space.

[Means for solving problems]

In order to achieve the above object, the hydrocarbon pyrolysis furnace according to the present invention is a pyrolysis furnace in which a reaction tube for a process fluid is arranged in a furnace, wherein the reaction tube has two paths on the inlet side and one on the outlet side. The present invention is characterized by a vertical tube arrangement structure in which the paths are joined together in the furnace and have no bend portion.

[Action]

According to the present invention, it is possible to reduce the pressure loss by forming a combined coil having a multi-pass small-diameter pipe on the coil inlet side and joining at an intermediate portion, and arranging it in a vertical pipe arrangement structure without using a bend. .

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

First Example In this example, the inlet side of the piping in the furnace is arranged at the lower part of the furnace.

FIG. 1 shows a conceptual diagram of a pyrolysis furnace according to an embodiment of the present invention. The furnace 2 has a shape in which the lower part is wide and the upper part is narrow, and the radiant coil 3 is arranged in the lower part in the width direction of the furnace 2.
Are arranged in columns. These are arranged in a line in the middle part of the furnace via a curved tube on the longitudinal center of the furnace. From the bottom of the furnace, burners 4 are arranged in three rows so that each radiant coil 3 is heated uniformly from both sides, and burners 8 are separately arranged for the same purpose even after the coils are arranged in one row. In addition, the burners 4 and 8 arranged in two stages enable control of the amount of heat transfer on the inlet side and the outlet side of the coil to some extent.

FIG. 2 is an explanatory view showing the shape of the radiant coil.
As shown in FIG. 3, the method of merging the coils can be such that the inlet side is multi-passed with two or more passes, the outlet side is merged into one pass, and the outlet side is merged again to guide it to the subsequent quencher. Incidentally, FIG. 3 (a) shows a 4-2-1 coil,
(B) shows a 6-2-1 coil.

The operation of this embodiment will be described with reference to FIG. After being preheated by the convection coil 6, the process fluid is introduced into the furnace from the hearth 9 of the furnace 2 through the crossover pipe 7 in two rows in the longitudinal direction of the furnace. The radiant coil 3 uses the hearth part as an inlet part, and rises up to the middle part in the furnace 2, where it is joined by a curved pipe and a confluent fitting and rises in a single row on the center of the furnace longitudinal direction, Ceiling 10
Will be introduced to the subsequent Quencher 5 through. The radiant coil 3 may be rejoined for each adjacent coil at the outlet of the upper part of the furnace as shown in FIG. In the lower part of the furnace 2, burners 4 are installed on both sides of the radiant coils 3 arranged in two rows, and the coils can be uniformly heated. Adjustment burners 8 are installed on both sides of the coil on the coil outlet side of the upper part of the furnace. According to this structure, as shown in FIG. 16B, the fluid temperature is rapidly increased on the coil inlet side, while the burner 4 is appropriately selected for the multi-pass, small-diameter tube. In addition to being achievable, adjustment can be performed on the outlet side by controlling the adjusting burner 8. Depending on the required degree of the fluid temperature distribution, the coil can be selected as shown in FIG. FIG. 4 shows the pressure distribution inside the pipe of the radiant coil 3, where A shows the case of the conventional coil,
The pressure loss of the bend part accounts for about 30% of the whole,
With the coil of this example, it is possible to eliminate most pressure loss in the bend portion as in B.

According to the present embodiment, in order to increase the amount of heat transfer at the coil inlet side, a small-diameter pipe and multiple passes are configured, and the initial purpose is not used without using 180 ° bends that affect the pressure loss inside the pipe. Can be achieved. Also, by arranging the lower part of the furnace (on the coil inlet side) in a two-row arrangement, the installation space can be halved compared to the case of the conventional one-row arrangement. However, the effect is extremely large in that it can be easily arranged in this embodiment.

Second Example The present example is a case where the inlet side of the piping in the furnace is arranged in the upper part of the furnace.

FIG. 5 is a conceptual diagram of a pyrolysis furnace according to another embodiment of the present invention. In the figure, the main body 1 has central radiant coils (reaction tubes) 12 and 13 arranged vertically. The burner 4 sandwiches the coil and is arranged on both sides, and the adjusting burner 8 is arranged in the ceiling arch portion. The raw material hydrocarbons are preheated by the convection coil 6 in the convection bank 6'and penetrate the ceiling 10 from the radiant coil inlet to radiant coil 13
Flowing in, vertically descending, coalescing with a bend 14 in the middle and further descending vertically, the coil 12 penetrates the hearth from the outlet and is quenched at Quencher 5, and the sensible heat is recovered as high pressure steam by the steam drum 15. , Decomposed gas 16. If necessary, the combustion exhaust gas is discarded from the stack 20 to the atmosphere via the IP / heater 18 and the IDF 19.

The coil has a fork-shaped form shown in FIG.
As shown in the figure, they are arranged continuously in the longitudinal direction of the furnace. Sixth
When the coil arrangement is viewed from the AA direction in the figure, one-row online formation is performed as shown in FIG. 7, and when viewed from the BB direction in FIG. 6, a two-row zigzag arrangement is obtained as shown in FIG. ing. The portion of the furnace in which the coils 13 are arranged has a side wall 24 formed immediately above it so as to occupy the flow path of the combustion gas as shown in FIG. Therefore, all of the coils 12 are in the furnace and the heating method is mainly radiant heat transfer, and most of the coil 13 is mainly convection heat transfer. If necessary, the heat transfer is further promoted by providing the longitudinal fins 25 of the coil 13 as shown in FIG.

Explaining the form of heat transfer here with reference to FIG. 10, the start of the reaction is in the convection zone, and a considerable reaction is proceeding at the entrance of the radiant heat transfer section. Since the reaction heat is constant, the absolute amount of heat transfer in the furnace becomes small, and therefore the amount of fuel input can be reduced. In addition, since the reaction tube requires the minimum required tube diameter and tube length, the ceiling is higher than in the conventional method, and the reaction tubes (coils) 12 and 13 are
Naturally, the overall height of the can be quite high.

〔The invention's effect〕

As described in detail above, according to the present invention, the inlet side of the coil is formed of a multi-pass small-diameter tube and the tubes are joined at the intermediate portion. In a so-called combined coil, it can be arranged without using a bend, the pressure loss can be reduced, and the installation space can be significantly reduced as compared with the conventional method. In addition, when the entrance side has three or more passes, it is possible to use a structure that cannot be arranged due to the structure in the conventional one-row arrangement. Further, since the inlet side and the outlet side are separated vertically, the control of the amount of heat transfer is improved compared to the conventional method, and it can be approached by optimization.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a pyrolysis furnace structure according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of a piping example thereof, FIG. 3 (a),
(B) is a diagram showing an example of the pipe shape, FIG. 4 is a diagram showing the relationship between the pipe length direction and the pressure distribution in the pipe, FIG. 5 is a diagram showing another embodiment, and FIG. 6 is the pipe confluence part. Explanatory drawing showing
6 is a sectional view taken along the line AA of FIG. 6, FIG. 8 is a sectional view taken along the line BB of FIG. 6, FIG. 9 is a sectional view when fins are provided in the pipe, and FIG. 10 is the other embodiment described above. Showing temperature characteristics of the pyrolysis furnace according to FIG. 11, FIG. 11 is a view showing an example of pipe shape, FIGS. 12 and 13 are conceptual diagrams of a conventional pyrolysis furnace, and FIG.
(D) is a diagram showing an example of the pipe shape, FIG. 15 is a diagram showing a heat flux distribution in the pipe length direction, and FIG. 16 is a diagram showing a pipe fluid temperature distribution in the pipe length direction. 1 ... Decomposition furnace main body, 2 ... Furnace, 3 ... Radiant coil (reaction tube), 4 ... Burner, 5 ... Quencher, 6 ...
… Convection coil, 9 …… hearth floor, 10 …… ceiling, 12 …… reaction tube (radiating section), 13 …… reaction tube (convection section), 14 …… 2 or bend, 24 …… side wall, 25 …… fin.

Claims (1)

[Claims] 1. A pyrolysis furnace in which a reaction tube for process fluid is arranged in a furnace, wherein the reaction tube has two paths on the inlet side and one path on the outlet side, and the paths merge in the furnace. Moreover, the hydrocarbon pyrolysis furnace is characterized by having a vertical tube array structure having no bend portion.