KR870001905B1 - Apparatus for thermal cracking of hydrocarbon - Google Patents

Abstract

Hydrocarbon-contd. stream flows through the improved tube, and cracked at 700-950 deg.C (heater provided on the outer tube part). The tube consists of (A) outer lay and (B) lining, bimetal. Compsn. for (A) comprises C(0.01-0.6 wt.%), Si(0.1-2.5), Mn (0.1-2.0), Cr(20- 30), Ni(18-40), N(0.01-0.15) and Fe and/or Mo, W, Nb(0.1-5 wt.%). Compsn. for (B) comprises C(0.3-1.5 wt.%). Si(0.1-3.0), Mn(6-15), Cr(20-30), Ni(0.1-10), Nb(0-3.0), N(0.010.15) and Fe(bal.%). Thickness of lining alloy is 0.3-5mm.

Description

Pyrolysis device of hydrocarbon

1 is a schematic process flow diagram illustrating an example of a process according to the present invention.

2 is a schematic diagram illustrating an embodiment of a disintegration tube apparatus in a radiation-heating zone.

3 is a schematic diagram illustrating another embodiment of a disintegration tube apparatus in a radiation-heating zone.

4 is a graph illustrating the effect of temperature on the settling rate of carbon in two different nickel-containing cracking tubes.

The present invention relates to an improvement in the apparatus in which hydrocarbons are pyrolyzed to produce cracking products comprising olefins such as ethylene and propylene.

More specifically, the present invention relates to a device for pyrolysis of hydrocarbons used in the part of the device in which the material from which the improved tube is pyrolyzed is heated to the highest temperature during the pyrolysis.

In a conventionally known apparatus, a mixture obtained by combining aliphatic saturated hydrocarbons such as ethane and naphtha (hereinafter simply referred to as hydrocarbons) with steam includes pyrolyzing hydrocarbons and containing ethylene, propylene and / or other olefins having four or more carbon atoms. Heated to a high temperature that is effective to produce the pyrolysis product.

The device is used on a large scale to carry out the pyrolysis of hydrocarbons, which is the first step in the process of producing olefins such as ethylene, propylene, butadiene, which are useful as starting materials in many chemical processes.

The pyrolysis of hydrocarbons is relatively rapid, with the mixture flowing in parallel (referred to hereafter simply as the reaction stream) through a plurality of connected reaction tubes, while the reaction stream reaches the outlet of the reaction tube for a period of time. Heating to a temperature of 800-950 ° C. caused by the heat generated by burning the fuel outside of the furnace. Each reaction tube used for this purpose consists of a yale tube and a digestion tube. The preheating tube is installed in the convection-heating zone of the device. The reaction stream is preheated in a preheating tube at a temperature in the range of 450-550 ° C. by exhaust gases generated by the combustion of the fuel. The digestion tube is installed in the radiant-heating zone of the device. The reaction stream preheated in the cracking tube is further heated to a temperature of 800-950 ° C. by the radiant heat produced by the combustion of the fuel.

The diameter and length of the cracking tube may vary depending on the design of the pyrolysis device.

An appropriate number of disintegrating tubes, each with an internal diameter of 25-200 mm and a length of 8-100 m, is used in parallel. The reaction stream is fed to each reaction tube at the feed temperature, first heated in a preheating tube to gradually increase its temperature to 450-550 ° C., then enters the decomposition tube and further heated to increase its temperature gradually, resulting in a maximum temperature. In the range of 800-950 ° C.

The reaction stream is then discharged from the cracking tube as a pyrolysis product that can flow to the next process step.

It is necessary to apply a lot of heat to the reaction stream in the heating described above.

In particular, in the heating step in the cracking tube, a large amount of heat is urgently provided to bring the reaction stream to a predetermined high pyrolysis temperature and to supply the amount of heat required to generate pyrolysis of the hydrocarbon in a very short time of about 1 second. It is important.

Therefore, it is necessary to supply decomposition heat to a very large amount of heat per unit area of the inner surface.

As a result, the wall temperature of the cracking tube is generally at least 100 ° C. higher than the temperature of the reaction stream flowing through it. Thus, adjacent to the outlet, the temperature of the cracking tube reaches 1000 ° C. or higher. The internal temperature in the preheating tube is relatively low and the hydrocarbons are only slightly pyrolyzed, so there is no real problem in the choice of the material used to make the preheating tube. However, the reaction stream in the cracking tube should be heated to 800-950 ° C., so that the cracking tube should be heated to a temperature higher than the temperature mentioned above.

Pyrolysis of hydrocarbons occurs as a result of the gradual deposition of carbon formed by partial pyrolysis of hydrocarbons on the inner surface of the cracking tube, which is strongly generated in the cracking tube, thereby preventing heat transfer from the cracking tube to the reaction stream.

As a result, as the amount of carbon precipitated increases, the temperature of the cracking tube should be gradually increased to maintain the temperature of the reaction stream at the required level, up to the heat-resistance temperature limit of the final tube.

While it is desirable to continue to operate the device, the action will have to be broken from time to time to allow removal of carbon deposits from the cracking tube.

Carbon precipitated at high temperature is dispersed and passed through the fine structure of the decomposition tube material (a phenomenon known as bridging or carbonation) to make the material from which the decomposition tube is made.

In order to withstand the carbonization, it is necessary to use a tube material containing a large amount of nickel. In order to cope with carbon precipitation and addition phenomenon, in the known art, as a decomposition tube, carbon 0.01-0.6, wt%, silicon 0.1-2.5 wt%, manganese 0.1-2.0 wt%, chromium 20-30 wt%, nickel 18-40 wt% At least one additional element selected from the group consisting of molybdenum, tungsten and niobium, which are substituted with iron alone or with a portion of iron in iron and present in an amount in the range of 0.1-5.0% by weight. Centrifugally cast tubes made of austenite heat resistant steel with a composition consisting of are used.

Using this tube, decoking operation temporarily stops the operation of the device whenever the temperature of the decomposing tube increases to a predetermined predetermined temperature due to the increase in the thickness of carbon deposited on the inner surface of the decomposing tube (usually 30 It is sometimes done by flowing only steam or air, or mixtures thereof, through the cracking tube so that the precipitated carbon, which occurs occasionally in the range of from 120 to 120 days, can be vaporized and removed.

The present inventors have found that some inventors have promoted the precipitation of carbon on the inner surface of the cracking tube by nickel present in the cracking tube.

In addition, as a result of the research, the present inventors developed a new alloy composition to produce a decomposition tube containing a smaller proportion of nickel, and using this, precipitation of carbon on the inner surface of the decomposition tube compared to the decomposition tube made of a conventional alloy. It was found that this is reduced.

The new material also has a low carbonization reaction even though it contains a small amount of nickel. The composition may be formed into a disintegration tube by centrifugal casting and may be in contact with another tube or the like by welding.

In addition, the new material is slightly better in heat resistance than conventional austenitic heat-resistant steel, so the present inventors have a centrifugal cast (the inner surface of the decomposition tube that is centrifugally cast into a common austenite heat-resistant material for use in pyrolysis of hydrocarbons). Later, an improved disintegration tube was developed) to develop a bimetal or two-layer disintegration tube coated with the new material described above.

In particular, the use of such an improved decomposition tube can reduce the number of decocking reactions. This fact is described in Japanese Patent Laid-Open No. 198587/1983. The present inventors have further studied the use of the improved bimetal decomposition tubes described above in practical production facilities.

As a result, many new discoveries are described below. One of these new findings is that the effect of nickel on the inner surface of the cracking tube to accelerate carbon precipitation becomes active when the temperature of the reaction stream is above 700 ° C.

This fact is explained next in connection with FIG.

4 shows 20 mm x 20 mm x 3 mm each made of two different conventional disintegration tube materials, one containing 25 weight percent chromium and 20 weight percent nickel, the other containing 25 weight percent chromium and 35 weight nickel. This is a graph showing the test results processed using two kinds of test pieces with the size of.

These test pieces were installed on aluminum boats placed in an SUS-304 cylindrical reactor having a diameter of about 50 mm and a length of 1200 mm installed in an electric furnace. The mixture of ethane or ethylene and steam flows through a cylindrical reactor heated to a predetermined temperature. The amount of carbon precipitated on the test piece was measured assuming that the test piece was the inner surface of the decomposition tube. In Figure 4, the abscissa represents the temperature of the reaction stream (° C) and the ordinate represents the amount of carbon precipitated per hour, in mg, per cm ² of the specimen surface.

As can be seen from the graph, the amount of carbon precipitated at the temperature of the reaction stream below 700 ° C. is so small that it cannot be measured.

However, when the temperature of the reaction stream is higher than 700 ° C., the amount of precipitated carbon increases gradually as the amount of precipitated carbon increases. At temperatures below 700 ° C, the precipitated carbon is thought to be caused by the normal pyrolysis of hydrocarbons and nickel does not affect the acceleration of carbon precipitation, but at temperatures above 700 ° C the above-mentioned carbon precipitation increases with increasing temperature. And carbon precipitation is likely to accelerate the precipitation of carbon by increasing the effect of nickel. Therefore, unlike usual, carbon precipitates rapidly. In other words, if it is possible to eliminate the effect of nickel, which promotes the precipitation of carbon, it can be speculated that the disadvantages of the prior art processes due to carbon precipitation can be greatly reduced, but the temperature of the reaction stream is in the range of 700 to 950 ° C. It is only necessary to do it in part of the cracking tube.

Temperatures above the reaction stream of 950 ° C. are generally not used because the output of olefins is reduced in the next step of the pyrolysis process.

The improved cracking tube described in Japanese Patent Laid-Open No. 198587/1983 uses an alloy containing less nickel on the inner surface of the cracking tube to which the reaction stream comes into contact with the surface. Significantly reduces the effect of accelerating settling. However, the improved bimetallic decomposition tubes themselves are expensive because two centrifugal slip castings are required to make each tube. In addition, a number of disintegration tubes with different materials in the inner and outer layers can be joined as a weld to manufacture the actual dismantling device, requiring much manpower-time to perform this welding as compared to conventional welding. Therefore, the use of an improved bimetallic tube over the entire length of the disintegration tube in a real device is very expensive.

If the improved bimetallurgical tube is used only in the region where the reaction stream is at a temperature of about 700 ° C, the length of the modified bimetallic tube will be reduced to less than about 60% of the total length of the tube in many design examples, making the electrolyzer relatively inexpensive. It can also be cast and has the added benefit of using an improved bimetal decomposition tube.

The main object of the present invention is to further increase the benefits generated by the use of an improved bimetallic cracked tube, thereby increasing the yield of olefins as described below in the Advantage Description of the present invention.

The present invention is described in more detail below.

In the device of the present invention, the above-described improved cracking tube is disposed between the point of the cracking tube and the outlet of the cracking tube used in the radiant-heating portion of the device, where the temperature of the reaction stream flowing between them reaches 700 ° C as described above. Used.

However, the carbon precipitation of the inner surface of the decomposition tube varies along the length of the decomposition tube because it is not uniform in the longitudinal direction of the tube and the temperature is irregular. Irregular temperatures are thus considered to result in a difference in the relative position between the fuel burner and each point in the longitudinal direction of the cracking tube. Therefore, in the present invention, depending on the relative arrangement of the cracking tube and the fuel burner in the radiant-heating portion, (1) from the point where the temperature of the reaction stream reaches 750 ° C. to its outlet, or (2) the temperature of the reaction stream at 700 ° C. Improved bimetallic decomposition, using only an improved tube, up to a point of up to 800 ° C, or (3) in two or more parts in the cracking tube from the point where the temperature of the reaction stream reaches 700 ° C to its outlet. It is effective to use a tube.

The temperature of the reaction stream at the point where the reaction stream flows from the conventional tube to the improved bimetal tube when the modified bimetallic decomposition tube is partially used in the above-described manner, the reaction stream at the point where the reaction stream flows from the improved bimetal tube. It is possible to reduce the carbon settling of the inner surface of the cracking tube depending on the temperature, the temperature of the cracking tube itself in the part where the improved bimetallic tube is used and the length of the improved bimetallic tube used. In any of the cases described above, the effect of reducing the amount of carbon precipitated per unit length of the cracking tube in the area where the improved bimetallic tube is used is greater the higher the temperature of the reaction stream or the cracking tube itself.

An improved bimetallic decomposition tube for use in the device according to the invention (A) 0.01-0.6% carbon, 0.1-2.5% silicon, 0.1-2.0% manganese, 20-30% chromium, 18-40% nickel At least one element selected from the group consisting of molybdenum, tungsten and niobium, with 0.01-0.15% by weight of nitrogen and the remainder being iron or iron and elements substituted with a portion of iron and present in an amount ranging from 0.1-5.0% by weight (B) 0.3-1.5 wt% carbon, 0.1-3.0 wt% silicon, 6-15 wt% manganese, 20-30 wt% chromium, 0.1-10 wt% carbon, with an outer layer made of austenitic heat resistant steel Consisting of an inner lining layer made of an alloy with a composition consisting of%, niobium 0-3.0% by weight and 0.01-0.15% by weight of nitrogen and the remainder of iron, the bimetallic tube of which lining layer covers the inner surface of the outer layer is used. do. The reason why this latter alloy composition is suitable for the inner lining layer of the decomposition tube is already described in detail in Japanese Patent Laid-Open No. 198589/1983, and is not described herein. The thickness of the inner lining layer of the inner surface of the disintegrating tube may be preferably in the range of 0.3 to 5 mm.

The improved bimetallic decomposition tube can be produced by first casting the outer layer by centrifugal casting as described above, and after the outer layer has solidified in the mold, the second centrifugal casting is poured into the melt prior to the inner lining layer inside the layer of the casting. Is executed. In general, if the inner surface of the cast outer layer is rough or irregular after solidification, and if a small amount of alloy melt that is not sufficient to produce an inner lining layer having a thickness of less than 0.3 mm is poured on the inner surface of the outer layer, the inner surface of such outer layer is generally It is not covered and leaves a large portion of the outer layer exposed. In addition, since the heat resistance and strength are superior to that of the alloy for the inner lining layer, the increase in the thickness of the inner lining layer is not effectively produced in view of maintaining the strength of the improved tube. As a result, the inner lining layer having a thickness larger than 5 mm is undesirable because it leads to an increase in the weight of the decomposition tube, and not only reduces the heat-transfer effect of the tube to some extent, but also costs more than the cost required to manufacture the decomposition tube.

Even if the inner surface of the outer tube of the disintegration tube is completely covered with the inner lining alloy described above without exposing any part of the outer layer, the inner surface of the bimetallic tube will still be rough as it is produced by centrifugal casting. It is possible to use such a cracked tube having a rough inner surface without further treatment, but since the rough inner surface has a slight effect of promoting carbon precipitation, in actual use, prior to using an improved bimetallic cracked tube, It is recommended that several known machines work together to smooth the inner surface. As an example, it is preferable that the thickness of the inner lining layer is 0.5 to 3.0 mm after the smoothing operation is completed. To facilitate understanding, the present invention is described in more detail with reference to FIG. FIG. 1 is a process flow diagram illustrating an example of a process in which a hydrocarbon is thermally decomposed to produce a pyrolysis product containing olefins. In FIG. 1, reference numeral 1 denotes a convection-heating portion in which a hydrocarbon tube 2a, a boiler feed water preheating tube 2b, and a preheating tube 2c for a mixture of hydrocarbons and steam are disposed. It is installed in the required heat-transfer zone.

Reference numeral 3 denotes a radiation-heated portion in which the disintegration tube 3a is disposed. A plurality of fuel burners 4 for heating the cracking tube are arranged in the radiant-heated portion. The convection-heating part 1 and the radiating-heating part 3 have a flue 11 through the convection-heating part 1 via exhaust gas duct 10 through which the exhaust gas generated by the combustion of fuel in the burner 4 passes. Through) to be released.

Two distinct examples of the device of the disintegration tube 3a in the radiation-heating part are shown in FIGS. 2 and 3.

In FIG. 2, the decomposition tube 3a consists of a tube in which a reaction stream flows from its inlet to its outlet. In FIG. 3, the decomposition tube is configured so that the incoming reaction stream flows through four parallel tubes 3b, 3c, 3d, and 3e.

At the tip of tube 3b-3e, the reaction stream is heated to a constant temperature.

The streams in the tubes 3b and 3c and the streams in the tubes 3d and 3e are combined and flow into the tubes 3f and 3g, respectively.

The reaction stream is heated to a predetermined temperature in the tubes 3f and 3g, combined, and flows into the tube 3a to be discharged at its discharge end.

Thus, many types of arrangements of dissociation tubes can be equipped with anything that can be used in the present invention. For the sake of simplicity the apparatus of a representative disassembly tube is described with reference to the tube 3a of FIG.

The hydrocarbon supplied to the hydrocarbon preheating tube 2a is preheated to a predetermined temperature by the exhaust gas generated by combustion of the fuel in the radiant-heating portion 3.

The preheated hydrocarbon thus combines with the steam supplied through the dilution steam supply conduit 2d.

The combined stream enters the mixture preheating tube 2c in which the product mixture is preheated to a temperature in the range of 450-550 ° C. while passing through the mixture preheating tube 2c.

The preheated mixed reaction stream is fed to a decomposition tube 3a which is further heated to produce a decomposition product. The product is then fed from the steam separator 6 via conduit 8a to a cooling heat-exchanger 5 which is indirectly cooled with hot water at its boiling temperature supplied under pressure. The cooled sea product is discharged to the next stage (not shown in the figure) through the conduit 7 which is further cooled to near-ambient temperature.

Condensable components having a relatively high boiling point are usually separated from the decomposition product into condensation during the cooling and uncondensed decomposition products are usually carried out to a low temperature separation unit such that they are pressurized to separate into each component. On the other hand, the pressurized hot water used for cooling the decomposition products in the heat exchanger 5 is converted into a mixture of hot water and steam and enters the steam separator 6 via the conduit 8b.

In the steam separator 6 the hot water is separated from the steam and circulated back to the cooling heat-exchanger 5.

The steam separated in the steam separator 6 is superheated with saturated steam or a suitable heat source and then discharged from the conduit 9 for use as any superheated steam for any desired purpose.

As described above, in the device of the present invention the above-described improved bimetallic tube is used in the part of the decomposition tube 3a in which the reaction stream has a temperature of 700 ° C or higher. Disintegration tubes incorporating broken bimetallic tubes can also be applied to various arrangements of disintegration tubes as shown in FIGS. Moreover, as described in the examples below, it has been found that the device of the present invention as a result of testing in actual installation has the advantages described below that were not expected before the test was performed. The first advantage of the device according to the invention is that the output of olefins is increased.

Increase in output of olefins-the reasons are not yet clear. However, the nickel atom exposed to the inner surface of the decomposition tube used in the prior art promotes catalysis in the reaction of consuming olefins such as pyrolysis or polymerization of olefins produced as a result of hydrocarbon decomposition. It is assumed to accelerate the precipitation of carbon on the inner surface of the tube.

For example, when naphtha is thermally decomposed using a cracking tube according to the present invention, the yield of olefins is increased by 1 to 5% by weight based on the starting naphtha, ie olefin is the addressing component of this kind of pyrolysis. The total amount of ethylene, propylene and olefins having four carbon atoms is 1 to 5% by weight higher than when the known decomposition tubes are used.

The unique olefin compounds that are most increased in yield vary with the pyrolysis temperature, length, and arrangement of the improved cracking tubes used therein.

This increase in olefins output is not large on the basis of a set, but is commonly used in large-scale plants producing 300,000 tonnes of ethylene and other olefins per year for this kind of pyrolysis at relatively low prices. To further increase the economic performance of the whole plate.

The second advantage of the present invention is that the blockage of the heat transfer zone of the cooling heat exchanger is reduced.

In the known process, heavy oil, which is part of the pyrolysis product, is attached to the heat transfer zone of the above-mentioned cold heat exchanger and carbonized to reduce heat transfer, make it difficult to cool the decomposition product, and increase the pressure drop in the heat transfer. In order to eliminate this problem, the device must be closed from time to time to remove the heavy oil deposited in the heat transfer zone.

However, the cleaning operation of the heat transfer zone needs to be performed less frequently than the decocking operation of the decomposition tube so that this is not considered a serious disturbance and can be carried out the same. Prior to testing the device of the present invention in an actual plant, the inventors expected that the number of decoking operations of the cracked tube would be reduced by the use of an improved tube, but the above-mentioned contamination of the heat transfer zone of the cold heat exchanger would not be changed.

Contrary to their expectations, the actual test indicated that the formation of heavy oil was 4-6% by weight, the amount formed in the known process based on the weight of the naphtha starting material, from 2-3% by weight with the use of an improved decomposition tube according to the present invention. Revealed a significant decrease.

Thus, the contamination of the heat transfer zone is also reduced. As a result, contamination of the heat transfer zone will not actually impede the operation of the device, and the continuous operation period of the device from the start after completion of the decocking operation to closing for the next decocking operation, as compared with the known art, is extended to a considerable extent. .

The third advantage of the present invention is that carbon precipitation is significantly reduced on the inner surface of the cracking tube because of the use of an improved bimetal cracking tube where the temperature of the reaction stream is above 700 ° C.

From the start of the decocking operation until it stops for the next decocking operation, the continuous operation value of the cracking device can be estimated at about 150 percent of the duration of the continuous process achieved in the known technical process, ie the continuous operation period. This is a 50 percent increase. Typically, the continuous operation period is 30-120 days in the known technology process but 45-810 days in the process according to the present invention. In a typical process, due to the relatively short duration of continuous operation, the 10-16 sets of Yale tubes, cracking tubes, cooling heat exchangers, combustion units for fuel, etc., described above, have been subjected to naphtha pyrolysis at the plant to produce 300,000 tonnes of ethylene per year. It must be installed.

A 10-16 cracking furnace is used as a reserve during the decocking operation. In contrast, the process of the present invention reduces the number of installed cracking furnaces to 8-14 in plants of the same capacity. In addition, it is necessary to use only partially modified bimetallic tubes for the entire length of the disintegration tube. Therefore, the unit cost of pyrolysis politics can be significantly reduced.

In the process of the present invention, ethane, liquefied petroleum gas, naphtha, gas oil and the like may be used as the hydrocarbon feedstock. In pyrolysis, 0.8-2.0 kg / cm ² G pressure can be used adjacent to the decomposition tube outlet.

The inlet pressure of the preheating tube is higher than the outlet pressure of the cracking tube by an amount corresponding to the amount of head loss required to flow the reaction stream through the preheating tube and the cracking tube.

It is preferred to add 30-80% by weight of steam relative to the amount of hydrocarbon feedstock for the purpose of reducing carbon precipitation to the extent possible during pyrolysis using the present politics. The holding period of the reaction stream in the cracking tube is in the range of 0.01 to 1 second, preferably 0.02 to 0.6 second. In addition, it is desirable to increase the temperature of the reaction stream to 800-900 ° C. at the outlet of the decomposition tube and to shorten the residence time of the decomposition tube relatively within the above range.

EXAMPLE

Three tests were conducted according to the process shown in FIG. In the first test, an improved bimetallic tube was used in the digestion tube from the point where the temperature of the reaction stream reached 700 ° C. to its outlet. A normal tube was used for the decomposition tube of the part whose temperature is 700 degrees C or less. In the second example, the improved bimetallic tube was used in the decomposition tube from the point where the temperature of the reaction stream reached 800 ° C. to the outlet thereof, and the conventional tube was used in the portion having the temperature below 800 ° C. Referred to as Example 2).

In the third example, a conventional tube was used for the entire length of the disintegration tube (hereinafter referred to as the comparative example).

In each of these three examples, the disintegration tube was constructed as shown in FIG. 2 and the total length of the disintegration tube was 80 m. Thus in Example 1 an improved bimetallic tube was used for the portion of the disintegration tube fitted from its outlet over a distance of 50m towards its inlet. In Example 2 an improved tube was used for the portion of the disintegration tube that was connected from its outlet over a 10 m distance towards its inlet.

Conventional tubes are made of austenitic heat-resistant steel made of 0.4% carbon, 2.0% silicon, 1.2% manganese, 25% chromium, 35% nickel, 0.05% nitrogen and the remainder of iron and have an inner diameter of 120- It was a 145 mm, 9 mm thick, centrifugally cast tube.

This conventional tube was welded and joined with a U-shaped casting made of an austenitic alloy as described above to form a smooth inner surface and form an arrangement as shown in FIG.

The inner diameter of the cracking tube gradually increases from the inlet towards its outlet.

The improved bimetallic tube used in accordance with the present invention is made using a centrifugally cast tube made of an austenitic alloy having a composition as described above, with an inner lining layer of 0.5 wt% carbon and 2.0 wt% silicon. It is coated by centrifugal casting with an alloy having a composition consisting of 9.0% by weight manganese, 25% by weight chromium, 3.0% by weight nickel, 0.3% by weight niobium, 0.05% by weight nitrogen and the remaining iron.

The resulting bimetallic tube was welded and joined by a U-shaped casting similar to that described above to smoothly process the inner surface and form an arrangement as shown in FIG. The improved bimetallic tube had a thickness of 9 mm on the outer layer and an average of 1 mm on the lining layer, and the inner diameter of the inner lining layer was 130-145 mm.

When using a cracking tube, the temperature of the reaction stream was measured by thermocouples inserted at appropriate intervals in the bends of the cracking tube.

In each of the three examples described above, a preheated and decomposed mixture of a naphtha vapor with a boiling point in the range of 136-150 ° C. and a specific gravity of 0.69-0.70 and a vapor with a weight of 0.5 for feed naphtha was preheated and decomposed to a temperature of 520-540 ° C. Fed into the tube. In the cracking tube of naphtha pyrolysis, the reaction stream was carried out by controlled combustion of the fuel so that the temperature of the reaction stream could be adjusted to a temperature in the range of 825-835 ° C. at the outlet of the cracking tube.

The amount of precipitated carbon in the cracking tube and the cooling heat exchanger was measured by the pressure drop in the reaction stream between the inlet and outlet of the cracking tube and the decomposition product stream between the inlet and outlet of the cooling heat exchanger, respectively.

The pyrolysis product was analyzed by indirectly cooling the sample obtained at the outlet of the decomposition tube and analyzing the uncondensed gas and condensate formed by gas chromatography.

The measurement results are shown in the following table.

TABLE 1

Embodiments of the invention, in which unique features and privileges are exemplified, are defined as follows.

TABLE 1

Claims (4)

In a pyrolysis station, a hydrocarbon-containing reaction stream is passed through a tube and heated to a high temperature by a heat source installed outside the tube, whereby the portion of the tube in which the temperature of the reaction stream is in the range of 700 ° C. to 950 ° C. is 0.01 carbon. -0.6% by weight, 0.1-2.5% silicon, 0.1-2.0% manganese, 20-30% chromium, 18-40% nickel, 0.01-0.15% nitrogen and the rest iron or iron, molybdenum, tungsten, An outer layer made of austenitic heat resistant steel having a composition consisting of 0.1 to 5.0% by weight of at least one element selected from the group consisting of niobium and 0.3-1.5% by weight of carbon, 0.1-3.0% by weight of silicon, 6-15% by weight of manganese Inner lining layer with a thickness of 0.3 to 5 mm, made of an alloy with a composition consisting of 20-30% by weight of chromium, 0.1-10% by weight of nickel, 0-3.0% by weight of niobium, 0.01-0.15% by weight of nitrogen and the remainder of iron Done by And the lining layer is made of a bimetal tube covering the inner surface of the outer layer. The pyrolysis politics of hydrocarbon according to claim 1, wherein the bimetal tube extends 10 to 50 meters from the discharge end of the tube toward the inlet end thereof. The pyrolysis politics of hydrocarbons according to claim 1, wherein the bimetal tube is located in the radiant heating part of the furnace. In a pyrolysis method of hydrocarbons, a hydrocarbon-containing reaction stream is flowed through a tube and the temperature of the stream is gradually raised until the temperature reaches at least about 700 ° C. and the temperature of the reaction stream is in the range of 800 ° C. to 950 ° C. The stream flows through a portion of the tube that is further increased, the portion being 0.01-0.6% carbon, 0.1-0.25% silicon, 0.1-2.0% manganese, 20-30% chromium, nickel 18 -40% by weight, 0.01-0.15% by weight of nitrogen and the remainder being made of austenitic heat-resistant steel with a composition consisting of 0.1 to 5.0% by weight of at least one element selected from the group consisting of iron or iron and molybdenum, tungsten, niobium 0.3-1.5 wt% carbon, 0.1-3.0 wt% silicon, 6-15 wt% manganese, 20-30 wt% chromium, 0.1-10 wt% nickel, 0-3.0 wt niobium, with thickness of 0.3-5mm % And an inner lining layer made of an alloy having a composition composed of 0.01-0.15% by weight of nitrogen and the remainder of iron, wherein the lining layer is made of a bimetallic tube covering the inner surface of the outer layer.

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