WO2016023745A1

WO2016023745A1 - Method for producing cracked gas containing ethylene and cracking tube for use in the method

Info

Publication number: WO2016023745A1
Application number: PCT/EP2015/067234
Authority: WO
Inventors: Maximilian Walter; Eric Jenne; Natalie GELDER
Original assignee: Basf Se
Priority date: 2014-08-13
Filing date: 2015-07-28
Publication date: 2016-02-18

Abstract

The invention relates to a method for producing cracked gas containing ethylene by thermally cracking a hydrocarbon or hydrocarbon mixture in the presence of water vapor in a cracking tube at temperatures in the range of 600 to 1000 °C and at a cracked-gas outlet temperature in the range of 750 to 1000 °C, wherein the cracking tube comprises a steel in the region through which flow passes first, which steel is an alloy containing 25 – 35 wt% chromium, 25 – 55 wt% nickel, 2 – 6 wt% aluminum, and 10 – 30 wt% iron, whereby deposits containing carbon are avoided in the tube, and the cracking tube has a catalytically active coating on the inner surface in the region through which flow passes thereafter, which catalytically active coating avoids deposits containing carbon in the tube, wherein the cracking tube does not have the catalytically active coating on the inner surface in the region through which flow passes first. The invention further relates to a cracking tube for use in the method.

Description

Process for the preparation of ethylene-containing cracked gas and can for use in the process

description

The invention relates to a process for the production of ethylene-containing cracked gas by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor in a can at temperatures in the range of 600 to 1000 ° C and a Spaltgasaustrittstemperatur in the range of 750 to 1000 ° C.

The invention further relates to a can for use in a process for the production of ethylene-containing cracking gas by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor. The thermal cracking of hydrocarbons in the presence of water vapor in a canned oven, in which usually the tubes are heated indirectly, finds widespread use in ethylene plants (steam crackers), in which in addition to the ethylene, other valuable unsaturated compounds such as propylene and butadiene and Pyrolysis gasoline with a high proportion of aromatic hydrocarbons such as benzene, toluene and xylene are won. The development of the process has led to ever shorter residence times in the crevices of the canned oven and to ever higher gap temperatures. In the modern process, residence times for the hydrocarbons in the cans of the can furnace of 0.1 to 0.6 seconds (s) and outlet temperatures of the cracked gases from the cans of more than 750 ° C., generally between 800 and 1000 ° C., are preferred , complied. See, e.g. D. Glietenberg et al., Ullmanns Encyklopadie der technischen Chemie, 4th ed., Volume 8,

Pages 158-194 (ethylene), Verlag Chemie, Weinheim, 1974, and L. Kniel, O. Winter, K. Stork, Ethylene: Keystone to the Petrochemical Industry, Marcel Dekker Inc., New York, 1980.

Although the thermal cracking of hydrocarbons in the presence of water vapor has reached a high technical level, the process has a considerable disadvantage, namely the formation and deposition of carbonaceous substances, esp. Coke, on the inner walls of the cans and the associated, So associated, molded parts in the canned oven, also called coking. Due to the insulating effect of these deposits, esp. Of the coke, increases the tube wall temperature of the split tubes and the associated moldings and the pressure loss increases.

In these extreme conditions finds

without the use of very special materials,

without special geometrical change of the crevice inner surface for deposit-preventing manipulation of the near-wall flow or

without special coating of the inner surface

a

Accelerated strong coking of the split tubes and associated moldings and a carburization and thus metallurgical change of the material of the split tubes and the associated moldings

instead of resulting in production limitations (throughput) and production time limitations (operating interval) as well as in the overall service life of the cans and the associated molded parts.

If the deposits, esp. Coke deposits, reached a certain strength, the canned oven must be turned off and the crevices of the deposits, esp. The coke, freed. The split tubes and associated moldings are usually freed of the deposits with a water vapor / air mixture or even only with air at temperatures of 700 to 1000 ° C, as for example. in EP 36151 A1 (BASF AG).

In order to effectively prevent, or at least significantly reduce, deposits, especially coke deposits, numerous different improvements have been developed and introduced to the market over the years. Among them are the following:

Catalytically active coatings on the inner surface of cans or canned systems which can significantly reduce carbonaceous deposits, especially coke deposits, and convert these deposits, especially coke, into CO and CO2, e.g. Camol ™.

See Petrone, Y. Chen, R. Deuis, L. Benum, D. Ghent, R. Saunders, C. Wong: Catalyst-Assisted Manufacture of Olefins (CAMOL): Realizing Novel Operational Benefits from Furnace Coil Surfaces AIChEe 2008 Spring National Meeting, New Orleans, Louisiana (08.04.2008);

S. Petrone, R.L. Deuis, F. Kong, P. Unwinn, CAMOL: Year- (4) Update on Commercial Furnace Installations, Presentation at the 2010 AIKhE Spring National Meeting, San Antonio, Texas (March 21-25, 2010),

M. Walter, S. Rech, CAMOL: Updated for use in naphtha service, 2013 AIChE Spring

Meeting (28.04.-02.05.2013),

WO 2013/181606 A1 (BASF Corporation),

BASF publication "CAMOL ™ catalytic coatings for steam cracker furnace tubes", BF-9657 3/12.

Geometric modifications of crevices or canned systems,

especially (a) by incorporation in the cans to provide altered flow conditions which reduce coking, e.g. Mixing Element Radiant Tube (MERT) and modifications thereof, such as sMERT and xMERT,

or especially (b) by bending the can to create altered flow conditions which reduce coking, such as e.g. Swirl Flow Tubes® (SFT®).

See (a): M. Györffy et al., MERT Performance and Technology Update, 2009 AIKhE Spring National Meeting (April 26-30, 2009), S. Matsueda, Next generation MERT achieves further advance in cracking tube performance, Hydrocarbon Asia, v. 15, n. 6, pp. 40-44, Nov. / Dec. 2005

WO 2004/046277 A1 (Kubota Corp.),

and to (b): M.W.M. Van Goethem et al., Enhanced Heat Transfer in Radiant Coils by Swirl Flow Tubes, AIChE Paper Number 94d for the Presentation at the 2014 Spring National

Meeting New Orleans, LA, 30.03.-03.04.2014,

CM. Schietekat et al., Swirl Flow Tube Reactor Technology: An Experimental and Computational Fluid Dynamics Study, Chemical Engineering Journal 238, pages 56-65 (2014), G. Zhang et al., Progressive Modern Pyrolysis Furnace Technology, Advances in Materi- als Physics and Chemistry 2, pages 169-172 (2012).

High-alloying, alumina-forming, Cr, Ni and Al-containing steels (ie Cr-Ni-Al-Fe alloys), and pipes preferably produced therefrom by centrifugal casting and moldings preferably produced from the similar alloys by means of casting , For example, an alloy containing, in particular,> 95% by weight (more particularly> 98% by weight) consisting of, 25-35% by weight chromium, 25-55% by weight nickel, 2-6% by weight % Aluminum and 10 - 30 wt .-% iron.

Cf .: Information Data Sheet, Centrailoy® HT E, Schmidt + Clemens GmbH + Co. KG, Sept. 2009, Rev. 01,

D. Jakobi et al., The High-Temperature Corrosion Resistance of Spun-Cast Meterials for

Steam Cracker Furnaces - A Comparative Study of Alumina and Chromia Forming Alloys, Paper no. 2287 for the NACE® Corrosion 2013 Conference & Expo,

D. Jakobi et al., Benefits from Educated Selection of Advanced Materials for Radiant Coils - A 10 Year Field Performance Review of Alumina Forming Alloys, AIChE Paper Number 152f for the Presentation at the 2014 Spring National Meeting New Orleans, LA, 30.03.-

04/03/2014.

Catalytically active coatings, e.g. CAMOL ™ have the disadvantage of all catalytic processes of being contaminated during operation with impurities, e.g. Sulfur compounds, and indefinite operating conditions in the canned oven lose activity.

US 5,242,574 A (Institute Francais du Petrole) relates to thermal vapor phase cracking and dehydrogenation of hydrocarbons in a honeycomb type reactor in a pyrolysis zone heated with a "heating liquid", in the presence of a special alloy 66-82 wt% Ni, 14-18 wt% Cr and 4-6 wt% Al.

WO 2014/092944 A1 (General Electric Company) describes the use of metallic cracker coils with an anti-coking catalyst layer, in particular perovskite (CaTiO 3), and an alumina barrier layer in the vapor-phase cracking of hydrocarbons.

The earlier application EP 14172815.4 dated 17.06.2014 (BASF SE) describes a process for the regeneration of a catalytically active coating on the inner surface of a crevice tube. res, which was previously used in a canned oven to produce ethylene-containing cracking gas, wherein the cracking gas was obtained by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor in the can at a Spaltgasaustrittstemperatur in the range of 750 to 1000 ° C, in the first at a Temperature in the range of 600 to 1000 ° C, an oxygen-containing gas mixture is passed through the can (step a), wherein a partial or complete removal of carbonaceous deposits takes place, and thereafter at a temperature in the range of 500 to 850 ° C, a gas mixture containing water vapor and passing hydrogen through the can at a load in the range of 0.01 to 0.4 kg H ₂ / (m ² catalytic coating * h) (step b).

The object of the present invention, while overcoming disadvantages of the prior art, is to provide an improved economical process for the production of ethylene-containing cracked gas.

In particular, the process should make it possible, by increasing the service life of crevices, to increase the production times for fission gas, e.g. between two decoking phases, to extend.

The method should also be particularly advantageous if a temperature range at which the catalytic coating has not yet reached the onset temperature is given in the inlet region of catalytic canned systems. (Onset temperature = minimum temperature for the effectiveness of the catalytic coating).

The process should also be particularly advantageous if, in the inlet region of catalytic canned systems, there is a temperature range at which the catalytic coating is not or only insufficiently restored after decoking, i. not or only insufficiently regenerated, can be.

Accordingly, a process for producing ethylene-containing cracked gas by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor in a can at temperatures in the range of 600 to 1000 ° C and a Spaltgasaustrittstemperatur in the range of 750 to 1000 ° C was found, which is characterized that

the can in the region through which it flows first comprises a steel which is an alloy containing 25-35% by weight chromium, 25-55% by weight nickel, 2-6% by weight aluminum and 10-30% by weight. % Iron, thereby reducing carbonaceous deposits in the pipe,

and the split tube in the subsequently flowed through area on the inner surface has a kataiytisch active coating which reduces carbonaceous deposits in the pipe.

Furthermore, a canned pipe has accordingly been found for use in a process for the production of ethylene-containing cracked gas by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor, esp. In the above-mentioned method, which is characterized in that the canned in first to be flown A steel comprising an alloy containing 25-35% by weight of chromium, 25-55% by weight of nickel, 2-6% by weight of aluminum and 10-30% by weight of iron, whereby carbonaceous deposits are reduced in the pipe in the manufacturing process for fission gas, and the gap in the subsequently flowing through area on the inner surface has a catalytically active coating which reduces carbonaceous deposits in the pipe in the production process for fission gas.

The canned tube according to the invention and the canned tube used in the method according to the invention therefore does not have the catalytically active coating on the inner surface in the region to be flowed through initially, but only in the region to be flowed thereafter.

Particularly preferably, the can in the region to be flown through does not comprise a steel as in the region to be flowed through first, but another steel which is particularly 0 to <0.5% by weight, in particular 0 to <0.1% by weight. Contains aluminum; an example is an alloy containing 25-45 wt .-% chromium, 30- 60 wt .-% nickel and 10-25 wt .-% iron; (The alloy may, for example, also niobium (eg 0.1 to 2 wt .-%) and / or carbon (eg 0.1 to 1, 5 wt .-%) and / or silicon (eg 0.5 to 2.5 Wt .-%) and / or manganese (eg 0.1 to 2 wt .-%) contain; typical further trace elements (eg in each case 0.01 to 0.5 wt .-%) may be: Zr, Ti and / or rare earth elements).

According to the invention, it was recognized that the og. Task is solved.

Suitable starting hydrocarbons for the thermal cracking are ethane, propane, butane, liquefied petroleum gas (LPG), gasoline fractions such as mineral spirits, e.g. Light gasoline having the boiling range of about 30 to 150 ° C, gasoline (full-range naphtha), e.g. Gasoline with a boiling range of approx. 30 to 180 ° C, heavy gasoline, e.g. Heavy gasoline with the boiling range of about 150 to 220 ° C, kerosene, e.g. Kerosene with the boiling range of about 200 to 260 ° C, gas oils such as light gas oil, e.g. light gas oil having the boiling range of about 200 to 360 ° C, heavy gas oil, e.g. heavy gas oil with the boiling range of about 310 to 430 ° C, and vacuum distillates. Furthermore, mixtures or combinations of suitable starting hydrocarbons can be used for the thermal cracking.

Preferred hydrocarbons for the production of ethylene-containing cracked gases are gases such as ethane, propane and mixtures containing ethane and propane, LPG, gasoline fractions, kerosene, bionaphtha, condensates, e.g. are obtained from gas fields, and / or gas oils and mixtures thereof.

In some of a high-alloy, on the inner surface of the tube alumina-forming, steel comprehensive and partly inside to be provided with a catalytically active coating crevices may be straight tubes or curved tubes, such as coils. The term 'split tube' in particular also includes molded parts connected to the split tube, such as Y-pieces, collectors, reversal bends, reducers.

Canned pipe plus connected moldings are also called canned system. In canned systems with one or more reversal bends, the region through which the flow passes is referred to as the first pass, the subsequently passed through passport area, and the second passage through which a further reversal arc passes, and so forth , Canned systems can be provided e.g. 1 to 20 reversal bends (or even more), especially e.g. 1 to 1 1 reverse bends, and corresponding to 2 to 21 (or correspondingly more), especially 2 to 12, passports. Passes in an initially traversed area can also be divided into several, e.g. 2 to 25, parallel tubes and possibly reversal bends be divided. Example: The Linde PYROCRACK® 4-2 Canned Pipe System (Fig. 2) consists of 6 passports and 5 reversing bends, with 4 passages divided into 2 parallel pipes in an initially flown-through area.

These crevices and canned systems described herein in the previous three paragraphs are conventional, non-geometrically modified crevices and canned systems. The total length of the canned pipe is measured from the crevice pipe entrance to the crevasse pipe outlet, thus also over the total length of a canned pipe system. When sizing the length, only one pipe counts in parallel pipes connecting later in the run (e.g., via Y-pieces or collectors). The decisive factor is the shortest possible path length via the can system.

In the process according to the invention, the can is preferably heated indirectly in the canned oven, ie. the split tube is not heated directly by a flame, but indirectly via the heat radiation of a flame. The thermal cleavage of the hydrocarbon or hydrocarbon mixture is preferably carried out at temperatures in the range of 600 to 1000 ° C, especially 700 to 1000 ° C.

The thermal cleavage of the hydrocarbon or hydrocarbon mixture is preferably carried out in the first flow-through range at temperatures in the range of 600 to 800 ° C and in the thereafter flowed through at temperatures in the range of 700 to 1000 ° C.

The outlet temperatures of the cracked gas from the split tube are 750 to 1000 ° C, preferably 780 to 950 ° C, in particular 800 to 900 ° C. The residence times in the can are particularly 0.05 to 1 second (s), preferably 0.08 to 0.6 s, in particular 0.1 to 0.3 s. The heat loads of the cans in the canned oven are preferably 64 kW / m ² h to 128 kW / m ² h (40,000 to 80,000 kcal / m ² h), preferably 58 kW / m ² h to 81 kW / m ² h (50,000 to 70,000 kcal / m ² h). The weight ratio of water vapor to the hydrocarbon used or to the hydrocarbon mixture used is in the thermal cracking particularly in the range of 0.1 to 1, preferably in the range of 0.2 to 0.8, and more particularly in the range of 0.3 to 0th , 7th The pressure in the can is in the thermal cleavage especially 1, 5 to 5 bar, especially 1, 6 to 2.5 bar.

In the method according to the invention, the can in the region through which it flows first comprises a high-alloyed steel which forms aluminum oxide on the inner side of the tube. This has the effect of reducing carbonaceous deposits in the pipe.

(A steel is considered to be high-alloy if the mass fraction of its alloying elements totals more than 5%, see, for example, Römpp Lexikon Chemie, Volume 3, "Hochlegierter Stahl", 10th edition, 1997, G. Thieme Verlag; DIN 17006 (10 / 1949)).

In particular, the split tube in the region through which it flows first consists of a high-alloy steel which forms aluminum oxide on the inner surface of the tube.

Preferably, the split tube was made in the first through-flow region by a centrifugal casting process.

(Centrifugal casting is a casting process in which the metallic permanent mold is set in rapid rotation so that the casting metal (eg high-alloyed steel) is forced into the mold by centrifugal force.) The melt settles evenly (gas-free, without cavities and slag inclusions) the inner wall of the mold and forms after solidification hollow body (tubes, cans, rings and the like); Römpp Lexicon Chemistry, Volume 5, "centrifugal casting", 10th edition, 1998, G. Thieme Verlag).

Preferably, the molded parts of the can system were produced by means of a casting process from the same steels.

In particular, the steel is a Cr, Ni and Al-containing steel, i. Cr-Ni-Al-Fe alloy.

Very particular preference is given to an alloy containing, in particular,> 95% by weight (more particularly> 98% by weight) consisting of, 25-35% by weight of chromium, 25-55% by weight of nickel, 2 6 wt .-% aluminum and 10 - 30 wt .-% iron. Further preferred is an alloy containing, in particular to> 95 wt .-% (more particularly to> 98 wt .-%) consisting of 27 to 33 wt .-% chromium, 28 to 52 wt .-% nickel, 2.5 - 5.5 wt .-% aluminum and 12 - 28 wt .-% iron. The alloy containing Cr, Ni, Al and Fe may also contain, for example, niobium (eg 0.1 to 1% by weight) and / or carbon (eg 0.1 to 1% by weight); Typical further trace elements (eg in each case 0.01 to 0.5% by weight) may be: Mn, W, Si, Co, Mo and / or Ti. An example of such an alloy can be found in the Information Data Sheet, Centrailoy® HT E, Schmidt + Clemens GmbH + Co. KG, Sept. 2009, Rev. 01. See also the other references cited above.

The formation of aluminum oxide on the inner surface of the tube takes place in the presence of oxygen, especially at elevated temperature, e.g. B.> 100 ° C, in particular> 500 ° C, for example in the range of 550 to 1000 ° C instead.

According to the invention, the area through which flow passes first preferably has a length in the range of 15 to 60%, in particular 20 to 55%, very particularly 25 to 50%, in each case based on the total length of the can.

In particular, according to the invention, the area through which flows thereafter directly adjoins the region through which flow has taken place. This results in the preferred length of the then flowed through area from the o.g. Lengths for the area flown through first (total length = 100%). However, it is also possible that, e.g. also by design, between the two areas a conventional area, e.g. over a length of> 0 to 20% (based on the total length of the can), without geometric modification and without catalytically active coating is located.

Preferably, the length of the first area flowed through increases with the residence time of the cracked gas in the can.

In particular, at residence times in the range of 0.10 to 0.60 s, the area flown through first preferably has a length in the range of 15 to 40%, especially 20 to 40%, very particularly 25 to 40%, in each case based on the total length of Canned tube, and has at residence times in the range of> 0.60 s (eg to 1 s) of the first flow-through range preferably has a length in the range of> 40 to 60%, especially> 40 to 55%, especially> 40 to 50 %, in each case based on the total length of the can.

In the process according to the invention, the concentration of hydrogen in the can in the location or in the region between the geometrically modified part and the catalytically active coated part is preferably in the range of 2 to 5% by volume, especially 3 to 4% by volume.

In the method according to the invention, the can in the region through which it flows first comprises a high-alloy steel which forms aluminum oxide on the inner surface of the pipe and in the region through which it flows, it has a catalytically active coating on the inner surface.

The catalytically active coating, which is applied in particular after the production of the can and before its use for thermal hydrocarbon cleavage on its inner surface, compared to a conventional can effect a reduction of carbonaceous deposits in the pipe.

Such catalytic cracking tubes and canned systems, also called "steam cracker furnace tubes with catalytic surface coatings", are also available on the market, see, for example, the above-mentioned Catalyzed-Assisted Manufacture of Olefins (CAMOL) systems. The "catalytically active coating" may also be referred to as a "catalytic coating", "catalyst layer" or as a "catalyst"; The catalyst is located as a layer on the inner surface of the can. The layer preferably has a thickness in the range of 0.05 to 5 mm, more preferably in the range of 0.1 to 3 mm, especially in the range of 0.2 to 2 mm.

Preferably, there is no aluminum oxide-containing layer between the catalytically active coating and the inner surface of the split tube, especially no layer consisting of aluminum oxide.

The catalytically active coating of the can contains as active component one or more metals of subgroups VIB, VIIB, VIII of the Periodic Table (Chemical Abstracts Service group notation), e.g. Cr, Mo, W, Mn, Re, Co, Ni. Preferably, these metals are present in the coating in oxidized form (oxidation number is> 0, especially in the range of 1 to 8, e.g., 2 to 7).

The catalytically active coating preferably contains manganese (Mn), especially manganese, in an oxidation state in the range from 2 to 7, further especially in the form of a manganese oxide, further especially in the form of MnO, Μη 2θ 3, MnC "2, Mn 2 C and / or Μη 3θ ₄ , especially in the form of MnO.

Particularly preferably, the catalytically active coating contains manganese (Mn), as stated above, and additionally tungsten (W), especially tungsten in an oxidation state in the range of 2 to 6, further especially in the form of a tungsten oxide, further especially in the form of W2O3, W0 ₂ , W0 ₃ , MWO4 (M = Be, Mg, Ca, Sr or Ba) and / or M3Y2WO9 (M = Be, Mg, Ca, Sr or Ba), especially in the form of CaW0 ₄ and / or Ba3Y2WOg.

Most preferred are CAMOL ™ coatings, as e.g. in the BASF publication "CAMOL ™ Catalytic Coatings for Steam cracker furnace tubes", BF-9657 3/12. These are the so-called "Low-Catalytic Gasification (LCG) Coating" and the so-called "High-Catalytic Gasification (HCG) Coating".

All pressure data refer to the absolute pressure.

Examples

1 shows schematically a canned oven including an inventive canned system with convection zone and radiation zone and quench cooler for the cracked gas. The canned system is located in the radiation zone.

Comparative Example 1 In a canned oven containing four canned systems, a mixture of 2.2 th of a gasoline fraction (naphtha) having a boiling range of 40 to 180 ° C and 1, 0 t / h of steam were passed per canned system and at a cracking tube outlet temperature of up to 840 ° C thermally split.

A canned system consists of 18 parallel, vertical inlet tubes, which are flowed through from top to bottom and merged into a manifold. From there, the fission gas is led out of the furnace in 2 parallel, vertical outlet pipes, which are flowed through from bottom to top. The canned system is constructed analogously to a selective 2-pass canned system with the designation SRT®-V from CB & I (Lummus); see. Fig. 3. The cracked gas from each of two split-tube systems is cooled in a downstream split-gas cooler.

The cracking tubes were internally provided with a catalytically active coating containing manganese, as described in the BASF publication "CAMOL ™ catalytic coatings for steam cracker furnace tubes", BF-9657 3/12. A combination of 'Low-Catalytic Gasification (LCG) Coating' in the front, first through-flow area, and 'High-Catalytic Gasification (HCG) Coating' in the rear, last flowed through area of the canned system was used. At the beginning of operation with naphtha, in clean canned systems, the manually measured pipe wall temperature at the outlet of the canned system was 940 to 980 ° C. The tube wall temperature at the measured location in the canned system eventually increased to 1 100 ° C after several months running time, the highest tube wall temperature used for the material and coating of this canned system. In the course of operation, the differential pressure of the flow nozzles in the inlet of the can system could be reduced to the minimum applied differential pressure limit of 0.3 bar.

In each case one of the criteria 'wall temperature' or 'differential pressure' could be decisive for the interruption of the production operation and the initiation of the decoking procedure.

For the decoking procedure, the hydrocarbon stream was interrupted by the canned oven and the canned systems separated from the process and freed from coke by means of oxygen. For this purpose, at a temperature in the range of 760 to 825 ° C and a pressure of 1, 05 to 3 bar over a total period of 60 hours at the beginning of a steam / air mixture passed into the gap tubes, which in the further course by reducing the

Steam quantity was changed so that the amount of air in the mixture of initially 10% by weight increased to 70 wt .-%.

example 1 In a canned oven containing four canned systems, a mixture of up to 2.2 t / h of a gasoline fraction (naphtha) having the boiling range of 40 to 180 ° C and 1, 0 t / h of steam are passed per canned system and at a crevice tube outlet temperature thermally split up to 840 ° C.

The split tubes are made in the front, first through-flow region of the can system from a high-alloy, produced by centrifugal casting, forming on the inner surface alumina steel, as described in the publication: Information Data Sheet,

Centrailoy® HT E, Schmidt + Clemens GmbH + Co. KG, Sept. 2009, Rev. 01. Composition of the alloy: 30% by weight Cr, 45% by weight Ni, 4% by weight Al, 0.45 Wt% C, 0.5 wt% Nb, 20.05 wt% Fe.

The aluminum oxide-forming high-alloy steel is provided, starting from the top, to a length of 40% of the total length of the can system. In the remaining rear, last flowed through, area of the canned system, the canned system is internally provided with a catalytically active coating containing manganese and tungsten, namely, High-Catalytic Gasification (HCG) coating, as described in the BASF publication "CMOL ™ catalytic Coatings for steam crackers furnace tubes ", BF-9657 3/12.

At the beginning of operation with naphtha, with a clean canned system, the manually measured pipe wall temperature at the outlet of the canned system can be 940 to 980 ° C. The tube wall temperature at the measured point in the last flowed through region of the crevice tube system can finally rise after several months of running up to 1 100 ° C, the highest pipe wall temperature applied to the material and the coating at this point of the canned system. In the course of operation, the differential pressure of the flow nozzles in the inlet of the can system can be reduced to the minimum applied differential pressure limit of 0.3 bar.

In each case one of the criteria 'wall temperature' or 'differential pressure' can be decisive for the interruption of the production operation and the initiation of the decoking procedure.

For the decoking procedure, the hydrocarbon stream is interrupted by the canned oven and the canned systems separated from the rest of the process and freed from coke by means of oxygen. For this purpose, at a temperature in the range of 760 to 825 ° C and a pressure of 1, 05 to 3 bar over a total period of 60 hours at the beginning of a water steam / air mixture passed into the gap tubes, which is changed in the further course by reducing the amount of steam so that the amount of air in the mixture of initially 10 wt .-% to 70 wt .-% increases. Through the combined application of the described technologies "high alloyed, at the

Pipe inner surface Alumina-forming "steel", in particular "alloy containing 25-35 wt .-% chromium, 25-55 wt .-% nickel, 2-6 wt .-% aluminum and 10-30 wt .-% iron", and "Catalytically active coating" carbon deposits are optimally reduced in the entire range of the canned system, so that extended by many days to several weeks extended production times of the canned oven, compared to the respective installed individual technology.

Claims

claims

A process for the preparation of ethylene-containing cracking gas by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor in a can at temperatures in the range of 600 to 1000 ° C and a Spaltgasaustrittstemperatur in the range of 750 to 1000 ° C, characterized in that the can in the first flowed through area comprises a steel which is an alloy containing 25-35% by weight of chromium, 25-55% by weight of nickel, 2-6% by weight of aluminum and 10-30% by weight of iron , which reduces carbonaceous deposits in the pipe, and

the canned in the area thereafter flowed through on the inner surface of a catalytically active coating which reduces carbonaceous deposits in the pipe, wherein the canned in the first through-flow area on the inner surface does not have the catalytically active coating.

A method according to claim 1, characterized in that the catalytically active coating contains manganese.

A method according to claim 1, characterized in that the catalytically active coating contains manganese and tungsten.

Method according to one of the preceding claims, characterized in that the can in the first through-flow area previously prepared by a centrifugal casting process.

Method according to one of the preceding claims, characterized in that the can in the region through which it flows first comprises a steel which is an alloy containing 27-33% by weight of chromium, 28-52% by weight of nickel, 2.5% - 5.5% by weight of aluminum and 12-28% by weight of iron.

Method according to one of the preceding claims, characterized in that the thermal cleavage of the hydrocarbon or hydrocarbon mixture in the first through-flow region at temperatures in the range of 600 to 800 ° C and then thereafter flowed through at temperatures ranging from 700 to 1000 ° C.

Method according to one of the preceding claims, characterized in that the first flow-through region has a length in the range of 15 to 60% based on the total length of the can.

Method according to one of the preceding claims 1 to 6, characterized in that the first flow-through region has a length in the range of 20 to 55% based on the total length of the can.

9. The method according to any one of the preceding claims, characterized in that the weight ratio of water vapor to the hydrocarbon used or to the hydrocarbon mixture used in the range of 0.05 to 1, 5 is.

10. The method according to any one of the preceding claims, characterized in that the thermal cracking is carried out at a pressure in the can in the range of 1, 5 to 5 bar.

1 1. Method according to one of the preceding claims, characterized in that the residence time in the can is in the range of 0.05 to 1 second.

12. The method according to any one of the preceding claims, characterized in that the can is in a canned oven and indirectly heated.

13. A can for use in a process for the production of ethylene-containing cracked gas by thermal cracking of a hydrocarbon or hydrocarbon mixture in the presence of water vapor, characterized in that the can in the first area to be flowed through a steel, which is an alloy containing 25-35 wt .-% chromium, 25-55 wt .-% nickel, 2-6 wt .-% aluminum and 10-30 wt .-% iron, whereby in the production process for fission gas carbonaceous deposits are reduced in the pipe, and the gap tube in the area to be flowed thereafter on the inner surface has a catalytically active coating which reduces carbonaceous deposits in the tube in the production process for fission gas, the gap tube not having the catalytically active coating on the inner surface in the region through which it flows first.

14. Canned tube according to the preceding claim, characterized in that the catalytically active coating contains manganese.

15. Canned tube according to claim 13, characterized in that the catalytically active coating contains manganese and tungsten.

16. Canned tube according to one of the three preceding claims, characterized in that the split tube in the first area to be flowed through was previously prepared by a centrifugal casting process.

17. Canned tube according to one of the four preceding claims, characterized in that the can in the region to be flowed through first comprises a steel, in which there is an alloy containing 27-33 wt .-% chromium, 28 - 52 wt .-% nickel, 2.5 - 5.5

Wt .-% aluminum and 12-28 wt .-% iron.

18. Canned tube according to one of the five preceding claims, characterized in that the first area to be flowed through has a length in the range of 15 to 60% based on the total length of the can.

19. Canned tube according to one of the preceding claims 13 to 17, characterized in that the first area to be flowed through has a length in the range of 20 to 55% based on the total length of the can.