TWI540120B - An ethylene cracking furnace - Google Patents

Description

Ethylene cracking furnace

The invention belongs to the field of petrochemical industry, and particularly relates to a furnace tube structure of an ethylene cracking furnace in petrochemical production.

In an ethylene plant, the cracking furnace is the core equipment. The design of the radiant furnace tube is the key to determining cracking selectivity, increasing the olefin yield of the cracked product, and increasing the suitability for different cracking feedstocks. Improving the structure and arrangement of the radiant coils has become the core part of the development of tubular cracking furnace technology. In the past 20 years, there have been radiant furnace tubes of different structures such as single-row branch reducer, mixed-row branch reducer, non-branch reducer, and single-pass equal-diameter.

The arrangement of the tubes is from the initial single row to the double row. For a single row, the same capacity requires a larger footprint. The advantage is that the circumferential temperature distribution of the tube is uniform, and there is less shielding. For the double row, the area of the cracking furnace is greatly reduced, but the shielding condition is serious, which affects the circumferential temperature distribution of the furnace tube.

In the patent CN1067669, the United States Lumm Crest Company announced its furnace tube arrangement, which has 6 tubes in the first pass and a tube in the second pass. The first pass tube passes through a manifold in the lower part. Two-way pipe connection. In this structure, since the first pipe is a plurality of pipes and the second pipe is one, when the furnace pipe is heated and expanded, the second pipe first expands downward, and the first pipe is pulled under the second pipe. Lower movement, wherein the force from the second tube is smaller, the force near the second tube is larger, and the lower tube is rigidly connected, and the difference between the second tube and the first tube is poor. It can only be adjusted by the balance system set at the inlet of the first pass. The result is that when the first pass cannot move with the second pass, the tube bends.

ExxonMobil Chemical Patents has published an arrangement in the CN1259981 patent, and another arrangement is disclosed in the US6528027 patent. The common disadvantage of the two structural tubes is that the lower portion of the first tube is inclined outward, and the second tube is not inclined in the opposite direction, and the adjacent first tube is inclined to the other side, and the result is in the furnace. When the tube is heated, the entire radiant tube is not well maintained in a single row and will naturally become a double row for stress relief. As a result, the sides of the furnace tube are unevenly heated, and the temperature of the tube walls on both sides is not equal. The temperature on the burner side is high and the side away from the side is low, causing the furnace tube to bend toward the burner side.

EP 1 146 105 discloses a cracking furnace in which the furnace tube structure is arranged: the two-way radiant section furnace tubes are vertically arranged in the radiant section furnace, and the straight tubes of the one-way tube and the two-way tube are arranged in one plane, one straight tube and The two-way pipe is connected to an elbow by an S-shaped pipe, and the S-shaped pipe of the one-way pipe and the two-way pipe are respectively parallel, and the connecting elbow may be semicircular, semi-elliptical or semi-oval, each elbow and straight The plane of the tube is at the same angle. However, the 2-1 type furnace tube has a Y-shaped tube in the lower part of the second tube in the first pass. Although the furnace tube arrangement overcomes the shortcomings of the above-mentioned furnace tube structure, the expansion of the two tubes connected with the Y-shaped tube is still caused. There will be differences and bends.

It can be seen from the above prior art that the existing furnace tube arrangement cannot avoid the deformation and deviation of the furnace tube, and the deformation causes the furnace tube to be unevenly heated, thereby further deforming and shifting the furnace tube, which is disadvantageous for improving. The rate of heat absorption and the resulting decrease in the life of the radiant furnace tube of the cracking furnace.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems in the prior art and to provide an ethylene cracking furnace having a two-pass radiant furnace tube capable of maintaining uniform heat, good mechanical properties and long life.

The invention is achieved by the following technical solutions: an ethylene cracking furnace comprising a high pressure steam drum, a convection section, a radiant section, a plurality of sets of radiant furnace tubes vertically arranged in the radiant section, a burner, and a quenching boiler; each radiant furnace tube comprises a first pass pipe and a second pass pipe and a connecting member for connecting the first pass pipe and the second pass pipe; the cracking material is introduced from the inlet end of the first pass pipe and is led out from the outlet end of the second pass pipe The first and second tube tubes are unbranched tubes, and the center lines of the tubes are on the same plane; the connecting member is a three-dimensional structural member including an inlet elbow, a return bend, and an outlet a bent pipe; one end of each of the first-pass pipes away from the inlet end thereof communicates with one end of an inlet elbow, and the other end of the inlet elbow communicates with one end of a return bend pipe, and the other end of the return bend pipe One end of the outlet elbow is in communication, and the other end of the outlet elbow is in communication with an end of the second leg pipe away from the outlet end thereof; the inlet elbow and the outlet elbow are respectively located in the first pass pipe and the second pass pipe furnace pipe The sides of the plane where the center line is located; a group The plane formed by the center line of the mouth bend intersects the plane formed by the center line of the set of outlet bends (end view), and the intersection line is located on the plane where the center line of the first pass pipe and the second pass pipe is located. And symmetrical about the plane; the return bends connecting the set of inlet bends and the set of exit bends are parallel to each other, and the plan view is a straight line segment of the same length; the side view projections of the connecting members are the same symmetrical continuous The curve is closed, and in order to meet the requirements of lowering the temperature and lowering the pressure drop during the cracking process under the same heat absorption rate, a variable diameter arrangement can be adopted for the radiant furnace tube. According to different needs, the variable diameter arrangement can take various forms (including but not limited to the following), wherein the first pass pipe and the second pass pipe length are the same in each form: (1) the first pass pipe The inner diameter of the second pipe is different from the inner diameter of the first pipe and the connecting member, and the inner diameter of the second pipe is larger than the inner diameter of the first pipe and the connecting member. It may be referred to as a primary variable diameter; (2) the first-pass pipe and the connecting piece have the same inner diameter, and the inner diameter of the lower portion of the second-row pipe is the same as the inner diameter of the first-pass pipe and the connecting member, and the second-pass pipe The inner diameter of the upper portion is larger than the inner diameter of the lower portion; (3) the first path tube has an equal diameter, the inner diameter of the connecting member is larger than the inner diameter of the first tube, and the inner diameter of the second tube is the same as the inner diameter of the connecting member; 4) The first pass pipe is of equal diameter, the inner diameter of the connecting piece is larger than the inner diameter of the first pipe, the inner diameter of the lower part of the second pipe is the same as the inner diameter of the connecting piece, and the inner diameter of the upper part of the second pipe is larger than the lower part of the connecting pipe. The inner diameter, which can be referred to as two variable diameters; (5) the first pass pipe is of equal diameter, the inner diameter of the connecting piece is larger than the inner diameter of the first pass pipe, and the inner portion of the second pass pipe More than the inner diameter of the connecting piece, the inner diameter of the upper portion of the second pass pipe is larger than the inner diameter of the lower portion; this may be referred to as three times of reducing; (6) the first pass pipe is a variable diameter, and the inner diameter of the first pass pipe is lower It is larger than the inner diameter of the upper portion of the first tube, and the inner diameter of the second tube is larger than the inner diameter of the lower portion of the first tube, which may be referred to as two variable diameters.

After adopting the above variable diameter arrangement, as the cracking reaction proceeds, the cross-sectional area of the radiant furnace tube is increased, the pressure drop of the tube tube is reduced (the partial pressure of hydrocarbon is lowered), the cracking reaction can be better satisfied, and the cracking performance is further improved. it is good. When the same cracking product yield is targeted, the cracking temperature can be effectively lowered, and when the same cracking temperature is reached, the yield of the target olefin product can be effectively increased.

In a preferred embodiment of the present invention, the first ones of the plurality of radiant tubes are parallel, the second tubes are parallel, and the first and second tubes are parallel; The plan view of the plane of the tube and the center line of the tube of the second pass tube is a straight line; the inlet bends are parallel, and the plan view projection is the same as the entrance angle of the straight line; the outlet bends are parallel, and the inlets are parallel The projection has the same exit angle as the straight line, and the exit angle is the same as the entrance angle.

In a preferred embodiment of the present invention, the first ones of the plurality of radiant tubes are parallel, the second tubes are parallel, and the first and second tubes are parallel; The plan view of the plane of the tube and the center line of the tube of the second pass tube is a straight line; the inlet bends are not parallel, and the top projection is different from the entrance angle of the straight line; the outlet bends are not parallel. The overhead projection is different from the exit angle of the straight line, but the exit angle of each radiant tube is the same as the inlet angle.

In a preferred embodiment of the present invention, the radiant furnace tube of the present invention may comprise at least one pipe section including a built-in spiral type twisted piece, the twisted piece being disposed in the pipe section along an axial direction of the pipe section Internally, the interior of the pipe section thus forms two spiral-shaped passages on both sides of the twisted piece, and the twisted piece is integrally formed with the pipe section.

Since the radiant furnace tube of the ethylene cracking furnace of the present invention adopts a pipe section having a built-in twisted piece, when the material flows through the surface of the twisted piece in the pipe section, the twisted piece forces the material to change from the original straight flow state to the spiral advancement. In the state, the material in the pipe section produces a lateral flow, which forms a strong flush on the pipe wall of the pipe section, so that the thickness of the boundary laminar flow layer with large thermal resistance is reduced, thereby improving the heat exchange effect. The improvement of the heat exchange effect causes the temperature of the inner wall of the radiant furnace tube to decrease, and the tendency of coking is reduced, which further improves the heat exchange effect.

In a preferred embodiment of the present invention, the twisted piece has a twist angle of between 100 and 360 degrees, and the twisted piece has an axial length of 180° twisted by a pitch, the pitch and the pipe section. The ratio of the inner diameter is between 2 and 3; the thickness of the twisted piece is similar to the thickness of the tube wall of the pipe section; in each cross section of the pipe section, between the twisted piece and the pipe wall of the pipe section Rounded corner transition.

In a preferred embodiment of the present invention, the radiant tube comprises a plurality of sections of the tube having a built-in twisted piece, and the sections of the sections having the built-in twisted piece are disposed at intervals in the radiant tube In at least one of the sections, the distance between the two adjacent sections of the tube having the built-in twisted piece is at least 5 pitches. Such an arrangement allows the total length of the tube section with the twisted sheet to occupy only a small portion of the entire radiant tube tube length throughout the tube process of the radiant tube. Therefore, there is no significant increase in the resistance of the material. Therefore, the cracking furnace using the pipe section can make the material spiral forward to enhance the heat transfer effect without significantly reducing the flow rate of the material in the radiant furnace tube.

Under the action of the twisted piece of the pipe section of the invention, the material in the pipe section produces a lateral flow, which forms a strong flushing of the pipe wall of the radiant furnace tube, so that the thickness of the boundary laminar flow layer with large thermal resistance is reduced, thereby reducing The resistance of the pipe wall to the flow of material helps to properly increase the advancement speed of the material.

Since the temperature of the inner wall of the radiant furnace tube of the cracking furnace is lowered, the service life of the radiant furnace tube of the cracking furnace is prolonged.

In the same way, the tubular cracking furnace of the radiant furnace tube with the tube section with the twisted piece can improve the heat transfer effect at a low cost, and can also increase the material handling amount.

According to a preferred embodiment of the present invention, the side view projection shape of the return bend of the radiant furnace tube of the ethylene cracking furnace of the present invention may be curved, semi-circular, semi-elliptical or parabolic.

In a preferred embodiment of the present invention, the set of radiant furnace tubes may include at least two of the radiant furnace tubes, and all of the first pass pipes and all the second pass pipes of each set of radiant furnace tubes are respectively concentrated. Arranged together.

In a preferred embodiment of the present invention, the second process tubes of the two sets of radiant furnace tubes may be arranged adjacent to each other to form a module; in the radiant section of the cracking furnace, a plurality of the modules are arranged, and each group The first pass tube and the second pass tube center line are all in the same plane.

In a preferred embodiment of the present invention, a plurality of sets of radiant furnace tubes may be arranged in the radiant section of the cracking furnace, and the first pass pipe of one set of radiant furnace tubes and the second pass pipe of another set of radiant furnace tubes are adjacent to each other Cloth, and the first pass tube and the second pass tube center line of each group are all in the same plane.

In the above structure, since the side view projection of each connecting member is a symmetrical continuous closed curve, the deformation of the connecting member is also symmetrical when heated, so that the heating is uniform and the single row remains unchanged. . Specifically, the two-way furnace tubes are located on the same plane, and the connecting members of the two-way furnace tubes are distributed on both sides of the plane where the furnace tubes are located, and the center of gravity of the furnace tubes is located in the plane, and the first and second tubes are respectively Concentrated arrangement, when the second-stage tube is expanded downward, the connecting piece and the first-row tube are regularly moved in the same direction, and in the hot state operation, the tube tube caused by the center of gravity of the tube not being in the plane of the tube can be avoided. The bending and moving directions are different, which can better ensure that the first-pass furnace tube and the second-pass furnace tube are in the center plane of the furnace to avoid the purpose of uneven heating. Therefore, the cracking furnace using the arranged furnace tube has the advantages of long operation period and good mechanical performance.

Each of the first process tubes in a set of radiant furnace tubes is parallel, each second process tube is parallel, and the first process tube and the second process tube are parallel; the furnace tube center line of the first process tube and the second process tube The plan view of the plane in which it is located is a straight line. The arrangement of the inlet elbow and the outlet elbow is various, one of which is: the inlet elbows are parallel, and the top projection is the same as the entrance angle of the straight line; the outlet elbows are parallel, and the top view is parallel The projection has the same exit angle as the straight line, and the exit angle is the same as the entrance angle. The other is that the inlet elbows are not parallel, and the top view projections are different from the entrance angles of the straight lines; the outlet bends are not parallel, and the overhead projections are different from the exit angles of the straight lines. A single exit angle is the same as the inlet angle.

According to different requirements, a group of radiant furnace tubes may include two or more of the radiant furnace tubes, and all of the first pass pipes and all the second pass pipes of each set of radiant furnace tubes are collectively arranged together. A plurality of sets of the radiant furnace tubes are arranged in the radiant section, and the arrangement thereof is various. One of them is: arranging two sets of radiant furnace tubes adjacent to each other to form a module, and two groups of The first process tube and the second process tube furnace tube center line are all in the same plane; in the radiant section of the cracking furnace, a plurality of the modules are arranged, and the first process tube and the second process tube furnace tube center of each group The lines are all in the same plane. The other is: the first pass pipe of one set of radiant furnace tubes is arranged adjacent to the second pass pipe of the other set of radiant furnace pipes, and the center line of the first pass pipe and the second pass pipe of each set are in In the same plane. In this arrangement, when the arrangement of the furnace tubes is an odd number, the first pass pipe and the second pass pipe can be arranged at intervals, and the furnace pipe is more uniformly heated in the radiant section furnace.

Depending on the situation, the twisted piece can be combined with the reducer to reduce the investment and improve the heat transfer effect. It can also be placed at the non-reducing pipe. The overall purpose is to make the reduction effect better and the cracking performance more. Favorable - extended operating cycle and increased olefin yield.

In the specific implementation, how many sets of furnace tubes are used depends on the capacity of the cracking furnace, which can be determined according to the raw material conditions, cracking furnace output, operating cycle and other design requirements.

In summary, the advantages of the present invention compared to the prior art are:

(1) Since the radiant furnace tube of the present invention adopts a variable diameter structure, especially a continuous multiple variable diameter arrangement, as the cracking reaction proceeds, the cross-sectional area increases, the tube pressure drop is reduced, and the purpose of reducing the hydrocarbon partial pressure is achieved. It can better meet the needs of the cracking reaction and has better cracking performance. When the same cracking product yield is targeted, the cracking temperature can be effectively reduced, and when the same cracking temperature is reached, the yield of the target olefin product can be effectively increased;

(2) Reduce the surface temperature of the furnace tube in actual operation, and the operation cycle is long, which can reduce the number of temperature rise and fall. The mechanical properties of the furnace tube are good and the furnace tube is not easy to bend. Therefore, the service life of the furnace can be extended for 2 to 3 years.

(3) As described above, since the radiant furnace tube of the ethylene cracking furnace of the present invention employs a pipe section having a built-in twisted piece, the ethylene cracking furnace of the present invention has a better heat exchange effect, reduces the tendency of coking, and has stable and reliable use performance. The life of the equipment is further extended.

The present invention will be further described in detail below with reference to the accompanying drawings:

As shown in Fig. 1, an ethylene cracking furnace of the present invention comprises a high pressure steam drum 1, a convection section 2, a radiant section 3, a plurality of sets of radiant furnace tubes 4 vertically arranged in the radiant section, a burner 5, and a quenching boiler 6.

As shown in FIG. 2, each radiant furnace tube includes a first pass pipe 7 and a second pass pipe 8 and a connecting member 9 for connecting the first pass pipe and the second pass pipe; The inlet end of the tube 7 is introduced and is led out by the outlet end of the second pass tube 8.

The first pass pipe 7 and the second pass pipe 8 are unbranched furnace tubes, and the center lines of the respective furnace tubes are on the same plane; the first pass pipe 7, the connecting member 9 and the second pass pipe 8 are at least changed. Trail once.

The connecting member 9 is a three-dimensional structural member, including an inlet elbow 10, a return bend 11 and an exit elbow 12; one end of each of the first pass tubes 7 away from the inlet end thereof is connected to one end of an inlet elbow 10 The other end of the inlet elbow 10 communicates with one end of a return bend 11 , and the other end of the return bend 11 communicates with one end of the outlet elbow 12 , and the other end of the outlet elbow 12 and the second pass tube 8 One end away from its outlet end is connected.

The inlet elbow 10 and the outlet elbow 12 are respectively located on two sides of the plane where the center line of the first tube 7 and the second tube 8 are located; the plane formed by the center line of the group of inlet tubes 10 is The planes formed by the centerlines of the set of outlet elbows 12 intersect, and the intersection line is located on the plane of the center line of the first tube 7 and the second tube 8 and is symmetric about the plane; a set of inlet elbows is connected 10 and a plurality of return bends 11 of the outlet elbow 12 are parallel to each other, and are projected in plan view as straight line segments of the same length, and the side view projection shape of the return bend pipe 11 is semicircular. The side view projections of the connecting members 9 are the same symmetrical continuous closed curve.

Each of the first pass pipes 7 in a group of radiant furnace tubes is parallel, each second pass pipe 8 is parallel, and the first pass pipe 7 and the second pass pipe 8 are parallel; the first pass pipe 7 and the second pass pipe The plan view of the plane of the center line of the furnace tube of 8 is a straight line. The arrangement of the inlet elbow 10 and the outlet elbow 12 are in various ways:

One of them is shown in FIG. 2: each of the inlet elbows is parallel, and the overhead projection is the same as the entrance angle of the straight line; the outlet elbows are parallel, and the overhead projection is the same as the exit angle of the straight line. The exit angle is the same as the inlet angle, and the angle is preferably 70 degrees.

The other is shown in FIG. 3: the inlet elbows 10 are not parallel, and the plan view projections are different from the entrance angles of the straight lines; the outlet elbows 12 are not parallel, and the plan view projections and the straight lines are formed. The outlet angle is different, the range of variation is 65-90 degrees, and the single furnace tube exit angle is the same as the inlet angle.

According to different requirements, a group of radiant furnace tubes may include two or more of the radiant furnace tubes, and all of the first pass tubes 7 and all the second pass tubes 8 of each set of radiant furnace tubes are respectively arranged in a concentrated manner. together. A plurality of sets of the radiant furnace tubes are arranged in the radiant section, and the arrangement thereof is various. One of them is: arranging two sets of radiant furnace tubes adjacent to each other to form a module, and two groups of The first process tube and the second process tube furnace tube center line are all in the same plane; the first set of the connector inlet elbow and the second set of the connector inlet elbow are in the first pass pipe and the second pass pipe cooker The two sides of the plane where the center line is located (as shown in Figure 4) or the same side (Figure 5); in the radiant section of the cracking furnace, a plurality of the modules are arranged, and the first pass tube 7 and the second pass tube of each group 8 furnace tube center lines are all in the same plane. The other is shown in Figure 6: the first pass pipe of one set of radiant furnace tubes is arranged adjacent to the second pass pipe of another set of radiant furnace tubes, and the first pass pipe and the second pass pipe cooker of each set The centerlines are all in the same plane.

In order to meet the requirements of lowering the temperature and lowering the pressure drop in the cracking process under the condition of the same heat absorption rate, the diameter of the radiant furnace tube can be reduced, that is, the diameter of the tube is gradually enlarged. According to different requirements, the variable diameter has various forms:

One of the first tube 7 and the connecting member 9 has the same inner diameter, and the inner diameter of the lower portion of the second tube 8 is different from the inner diameter of the connecting member 9, and the inner diameter of the upper portion and the inner diameter of the lower portion are also different (Fig. 7). .

The other is: the first pipe 7 is a variable diameter, the upper inner diameter is different from the lower inner diameter, the inner diameter of the connecting member 9 is the same as the inner diameter of the lower portion of the first pipe 7, and the second pipe 8 is equal diameter. (Figure 8).

There is also a case where the first path tube 7 has a variable diameter, the inner diameter of the connecting member 9 is the same as the inner diameter of the lower portion of the first path tube 7, and the inner diameter of the lower portion of the second path tube 8 is different from the inner diameter of the connecting member 9. The upper inner diameter and the lower inner diameter are also different (Fig. 9).

In the specific implementation, how many sets of furnace tubes are used depends on the capacity of the cracking furnace, which can be determined according to the raw material conditions, cracking furnace output, operating cycle and other design requirements.

The process performance comparison of different implementations using 48 radiant furnace tubes is as follows:

Comparative example: (equal diameter)

Example 1 (one-time reduction)

Example 2 (secondary reduction)

Example 3 (three-way reduction)

Further, as shown in Figs. 10 to 14, the present invention also employs a pipe section 100 with a twisted piece. As can be seen from the end face shown in Fig. 11, the pipe section 100 with the twisted piece includes the pipe wall portion 110 and the twisted piece portion 120. The twisted piece portion 120 is integrally formed with the tube wall portion 110 of the tube section. The twisted piece portion 120 divides the pipe section 100 into two material passages 130 and 140 having substantially the same cross-sectional area along the diametrical direction of the pipe section 100.

According to the idea of the present invention, in the material passages 130 and 140, at the joint portion of the twisted piece portion 120 and the pipe wall portion 110 of the pipe segment, that is, the corner portions indicated by reference numerals 5, 6, 7, and 8, The twisted piece and the pipe wall of the pipe section have a rounded transition, and the transition fillet is not too large, otherwise the passages 130 and 140 are too narrow, which may affect the flow of the material. On the other hand, the transition fillet should not be too small, otherwise the flowing material will form a dead-end vortex here, and local coking will easily form.

The length of the tube section with the twisted piece shown in Fig. 10 is one pitch. Therefore, the end view viewed along the arrow A or the arrow E is the same, as shown in Fig. 11, the twisted piece portion 120 on the end face is in a horizontal state.

Fig. 12 shows a cross-sectional view at a length of 1/4 from the left end of the pipe section 100 of Fig. 10, in which the twisted piece portion is inclined to the left by 45°.

Figure 13 shows a cross-sectional view at a length of 1/2 from the left end of the pipe section 100 of Figure 10, in which the twisted piece portion is in a vertical state.

Fig. 14 shows a cross-sectional view at a length of 3/4 from the left end of the pipe section 100 of Fig. 10, in which the twisted piece portion is inclined to the right by 45°.

In summary, the tube segment 100 with the twisted sheet according to the present invention has the same cross-sectional shape and size at any section along its axial direction. The only difference is that the angle of inclination of the twisted piece portion 120 is different. This reflects the twisted state of the twisted sheet.

The twisted piece 120 can be twisted left-handed or twisted right-handed.

The twisted sheet 120 can be either at a position along the diameter of the tube section or offset from the diameter of the tube section. When offset from the diameter position of the pipe section, the material passages 130 and 140 have different cross-sectional areas.

The cross section of the twisted sheet 120 may be in a straight state (as shown in Figs. 11 to 14) or in a curved state (not shown).

According to actual needs, the twisted piece can also be designed into a more complicated shape to divide the inner cavity of the pipe section into two or more material passages.

In the present invention, the term "pitch" S refers to the axial length of each twisted piece of 180°, and the term "twist ratio" Y refers to the ratio of S to the inner diameter D of the pipe section. That is: Y=S/D.

The smaller the Y value, the greater the degree of distortion of the twisted sheet. Therefore, the greater the lateral flow tendency of the material in the pipe section, the better the heat transfer enhancement effect and the greater the tendency to reduce the coking; however, if the Y value is too small, the material is too small. The resistance will increase, which will affect the flow rate of the material.

Conversely, the larger the Y value, the smaller the degree of distortion of the twisted sheet. Therefore, the smaller the lateral flow tendency of the material in the tube section, the smaller the resistance of the material, and the higher the flow rate. However, the weaker the heat transfer enhancement effect, the weaker the tendency to reduce the coking.

Therefore, it is especially important to choose the appropriate twist ratio. In the present invention, the twist ratio Y = 2.5 can achieve a good overall effect. A satisfactory overall effect can be obtained in the range of the twist ratio Y=2~3.

If a twisted sheet is provided over the entire length of the radiant tube of the cracking furnace, it is of course better for enhancing the heat transfer effect, however, the material resistance is increased, which affects the flow rate of the material. To this end, in the present invention, a pipe section with a twisted piece is provided in sections over the entire length of the radiant furnace tube of the cracking furnace, and an empty pipe section of a certain length is left between two adjacent pipe sections. After the material flows through the pipe section with the twisted piece and spirally flows, when the material enters the empty pipe section, the material can still flow spirally due to the flow inertia of the material.

The distance between two adjacent tube segments is at least 5 pitches. In a preferred embodiment of the invention, the distance between two adjacent said pipe segments is between 15 and 20 pitches.

It can be seen from Table 5 that the effect of adding the twisted tube is better, but the pressure drop is increased; compared with various different diameters, the more the number of reductions, the better the effect.

1. . . High pressure steam drum

2. . . Convection section

3. . . Radiation section

4. . . Radiant tube

5. . . burner

6. . . Quench boiler

7. . . First pass

8. . . Second pass

9. . . Connector

10. . . Entrance elbow

11. . . Back bend

12. . . Exit elbow

100. . . Pipe segment with twisted piece

110. . . Wall portion

120. . . Twisted piece

130. . . Material channel

140. . . Material channel

Figure 1: Schematic diagram of the cracking furnace of the present invention;

Figure 2 is a schematic front, side and top plan view of an embodiment of a set of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 3 is a schematic front, side and top plan view of a set of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 4 is a plan view showing a schematic arrangement of two sets of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 5 is a plan view showing a schematic arrangement of two sets of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 6 is a plan view showing a schematic arrangement of two sets of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 7 is a schematic elevational view of a set of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 8 is a schematic elevational view of a set of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 9 is a schematic elevational view of a set of radiant furnace tubes in accordance with one embodiment of the present invention;

Figure 10 is a schematic side elevational view of a tube segment with a twisted sheet, in which the positions of the B-B, C-C, D-D profiles are indicated, in accordance with one embodiment of the present invention;

Figure 11 is a schematic end view taken along arrow A or arrow E in Figure 10;

Figure 12 is a cross-sectional view taken along line B-B of Figure 10;

Figure 13 is a cross-sectional view taken along line C-C of Figure 10; and

Figure 14 is a cross-sectional view taken along line D-D of Figure 10.

7. . . First pass

8. . . Second pass

9. . . Connector

10. . . Entrance elbow

11. . . Back bend

12. . . Exit elbow

Claims (10)

An ethylene cracking furnace comprising a high pressure steam drum, a convection section, a radiant section, a plurality of sets of radiant furnace tubes vertically arranged in the radiant section, a burner, and a quenching boiler; each radiant furnace tube comprises a first pass pipe and a second pass a tube and a connecting member for connecting the first pass pipe and the second pass pipe; the cracking material is introduced from the inlet end of the first pass pipe and is led out from the outlet end of the second pass pipe; wherein: the first pass The tube and the second tube are unbranched tubes, and the center lines of the tubes are on the same plane; the connecting member is a three-dimensional structural member, including an inlet elbow, a return bend, and an outlet elb; each One end of the first pipe away from the inlet end thereof communicates with one end of an inlet elbow, the other end of the inlet elbow communicates with one end of a return bend, and the other end of the return bend communicates with one end of the exit elbow The other end of the outlet elbow is in communication with the end of the second path tube away from the outlet end thereof; the inlet elbow and the outlet elbow are respectively located on the plane of the center line of the first and second tube tubes Side; the centerline of a set of inlet bends The plane intersects the plane formed by the centerline of the set of exit bends, the intersection line is located on the plane of the center line of the first pass tube and the second pass tube tube, and is symmetric about the plane; connecting a set of inlet bends And the return bends of the set of outlet bends are parallel to each other, and the plan view is a straight line segment of the same length; the side view projections of the connecting members are the same symmetrical continuous closed curve, and the inner diameter of the radiant furnace tube One of the following combinations or The combination of the first tube and the connecting piece are the same, the inner diameter of the lower part of the second tube is larger than the inner diameter of the connecting piece, and the inner diameter of the upper part of the second tube is larger than the inner diameter of the lower part; (2) The first pipe is of equal diameter, the inner diameter of the connecting piece is larger than the inner diameter of the first pipe, the inner diameter of the lower part of the second pipe is the same as the inner diameter of the connecting piece, and the inner diameter of the upper part of the second pipe is larger than the inner diameter of the lower part (3) the first pass pipe is of equal diameter, the inner diameter of the connecting piece is larger than the inner diameter of the first pipe, the inner diameter of the lower part of the second pipe is larger than the inner diameter of the connecting piece, and the inner diameter of the upper part of the second pipe is larger than The inner diameter of the lower portion is (4) the first path tube is arranged in a variable diameter, the inner diameter of the lower portion of the first tube is larger than the inner diameter of the upper portion of the first tube, and the inner diameter of the connecting member is the same as the inner diameter of the lower portion of the first tube. The second path tube is of equal diameter, the second path tube inner diameter is larger than the connecting piece inner diameter; (5) the first path tube is of variable diameter arrangement, and the inner diameter of the first path tube is larger than the first The inner diameter of the upper portion of the tube is greater than the inner diameter of the connecting member. The ethylene cracking furnace according to claim 1, wherein each of the first pass pipes is parallel, each second pipe is parallel, and the first pass pipe and the second pass pipe are parallel. a top view projection of a plane of the center line of the furnace tube of the first pass pipe and the second pass pipe is a straight line; the inlet bends are parallel, and a top view projection is the same as an entrance angle formed by the straight line; The elbows are parallel, and the overhead projection is the same as the exit angle of the straight line, and the exit angle is the same as the The entrance angle is the same. The ethylene cracking furnace according to claim 1, wherein each of the first pass pipes is parallel, each second pipe is parallel, and the first pass pipe and the second pass pipe are parallel. The plan view of the plane of the center line of the furnace tube of the first pass pipe and the second pass pipe is a straight line; the inlet bends are not parallel, and the top view projection is different from the entrance angle of the straight line; The outlet elbows are not parallel, and their overhead projections are different from the exit angles of the straight lines, but the outlet angle of each radiant tube is the same as the inlet angle. The ethylene cracking furnace according to any one of claims 1 to 3, wherein the radiant furnace tube comprises at least one pipe segment including a built-in spiral type twisted piece, the twisted piece being along The tube segments are axially disposed inside the tube segments such that the interior of the tube segments form two helical channels on either side of the twisted sheet, the twisted sheets being integrally formed with the tube segments. The ethylene cracking furnace according to claim 4, wherein the twisted piece has a twist angle of between 100 and 360 degrees, and the twisted piece has an axial length of 180° per twist. The ratio of the pitch to the inner diameter of the pipe section is between 2 and 3; the thickness of the twisted piece is similar to the thickness of the pipe wall of the pipe section; in each cross section of the pipe section, the twisted piece There is a rounded transition between the pipe wall and the pipe section. The ethylene cracking furnace according to claim 5, characterized in that the radiant furnace tube comprises a plurality of sections of the tube having a built-in twisted piece, and the sections of the sections having the built-in twisted piece are spaced apart from each other. The method is disposed in at least one length of the radiant furnace tube, and the distance between the two adjacent sections of the tube having the built-in twisted piece is at least 5 pitches. The ethylene cracking furnace according to the first aspect of the invention is characterized in that the side view projection shape of the bendback tube is curved, semicircular, semi-elliptical or parabolic. The ethylene cracking furnace according to claim 1, wherein the set of radiant furnace tubes comprises at least two of the radiant furnace tubes, and each of the first radiant tubes of each group of radiant tubes and All the second pass pipes are arranged together in a centralized manner. The ethylene cracking furnace according to claim 1, wherein the second process tubes of the two sets of radiant tubes are arranged adjacent to each other to form a module; and in the radiant section of the cracking furnace, a plurality of said The module, and the first pass pipe and the second pass pipe center line of each group are all in the same plane. The ethylene cracking furnace according to claim 1, wherein in the radiant section of the cracking furnace, a plurality of sets of radiant furnace tubes, a first radiant tube and a radiant furnace tube are arranged The two-way tubes are arranged adjacent to each other, and the first-pass tube and the second-tube tube center line of each group are all in the same plane.