DE102007048984A1 - Process for the decoking of cracking furnaces - Google Patents

Abstract

The invention describes a process for decoking a cracking furnace (1) for the cracking of hydrocarbons. During decoking, a mixture of air and water vapor is sent into the cracking tubes (2) and the subsequent quenching gas coolers (3). During decoking, the radiation zone (1a) of the cracking furnace (1) is kept at a temperature of about 1100 ° C. via the burners (4). The resulting Entkokungsabgas (5) is passed to a cyclone separator (6). Before the cyclone separator (6) water (7) is injected at regular intervals in the Entkokungsabgas (5). In the cyclone separator (6), solid particles, such as coke particles or dust particles, are separated from the gaseous decoke exhaust gas (8). The freed from solid components Entkokungsabgas (9) is fed into the combustion chamber of the radiation zone (1a) of the cracking furnace (1). At the temperatures prevailing there, the carbon monoxide still present in the decoking exhaust gas (9) is almost completely converted to carbon dioxide. The slit furnace escaping exhaust gas (10) is thus now freed from coke or dust particles and carbon monoxide.

Description

The The invention relates to a process for decoking a cracking furnace for the thermal cracking of hydrocarbons, in which a Entkokungsgas passed through coked plant parts, with a decoking exhaust gas arises.

The thermal cracking of hydrocarbons, especially the thermal cracking directed to the formation of ethylene and other lower olefins, is of great industrial importance. As is known, cracking furnaces with at least one convection and radiation zone are used. The actual thermal splitting is carried out in the burner-heated radiation zone, while in the convection zone, the hydrocarbons and other fluids are heated by arranged there heat exchanger against the flue gas. Usually, hydrocarbon and process steam are preheated in the heat exchangers of the convection zone and fed to the arranged in the radiation zone coils a hydrocarbon / vapor mixture. In a downstream quench cooler, the generated cracking gases are rapidly cooled to stop the reactions. Such splitting methods and cracking furnaces are for example made DE 2830824 and DE 2854061 known.

at However, the implementation of such methods occur Series of side reactions that are too economically uninteresting or disturbing products. Such a thing annoying side reaction is the coking of plant components, in particular the split tubes and the quench cooler. There the coke deposited in the cans is an excellent one Heat Insulator is, goes with the coking with a significant deterioration the heat transfer and an increase in temperatures associated with the split tubes. The progressive coking and the so Associated increase in the tube wall temperatures of the split tubes are material engineering Set limits.

It is therefore necessary, the thermal decomposition from time to time to interrupt and perform a decoking of the plant. This is usually done by the supply of a decoking gas, z. B. from air and / or water vapor, which continue through the externally heated crevices and the still cooled Split gas cooler is performed. At the high temperatures the decoking, for example, between 600 ° C and 1050 ° C. lie, there is a burning of the deposits. Part of the deposits is discharged mechanically.

The thereby resulting Entkokungsabgas can z. B. Peak values up to about 20,000 ppm by volume of carbon monoxide in dry exhaust gas. An immediate release of this decoke exhaust gas to the atmosphere should therefore be avoided for environmental reasons.

After, in EP 0497155 As the prior art described method, the Entkokungsabgas for afterburning of the coke particles and the carbon monoxide is introduced into the furnace of the cracking furnace. Since the amount of Entkokungsabgases in relation to the resulting from the unterfeuerten power of the cracking furnace flue gas during decoking is large, a great deal of effort for a uniform supply of Entkokungsabgases must be operated over the entire furnace to operate the oven burner safely and trouble-free. For this purpose, a complex gas channel system is required. Additionally, at this, in EP 0497155 As described in the prior art, procedure performed a relatively large amount of exhaust gas into the furnace. This relatively large amount of exhaust gas must be heated, which increases the heating demand during decoking.

To avoid these disadvantages, is in EP 0497155 proposed not to lead the decoke exhaust gas into the furnace but to a catalytic treatment. By using a catalyst for the oxidation of incompletely combusted components in the decoking exhaust gas, the process is simplified. The carbon monoxide and other unburned components in the decoke exhaust gas are further reduced, but the mechanically discharged deposits remain in the decoke exhaust gas.

An alternative method of decoking a fission gas furnace and a subsequent quench cooler is disclosed in US Pat US 5186815 described. At the in US 5186815 described method, the hydrocarbon-containing feed is continuously fed solid particles having a diameter of less than 150 microns via a carrier gas. These small solid particles consistently pass through the split tubes and the quench cooler with the hydrocarbonaceous feed and provide for constant erosion of coke on the interior of the fission gas tubes or quench cooler. About a cyclone at the exit of the quench cooler, the solid particles are separated from the gaseous products of the cleavage and recycled back into the hydrocarbonaceous feedstock of the thermal cleavage.

Both prior art methods have disadvantages. At the in EP 0497155 described recycling of Entkokungsabgases into the furnace or to a catalytic treatment can be almost completely oxidize carbon monoxide to carbon dioxide, but the solid coke particles contained in Entkokungsabgas are not burned or removed. The dust or coke emission can therefore in a process after EP 0497155 sometimes well above the limit of 50 mg / Nm ^{3 of} the European emission standard.

In a procedure such as in US 5186815 Although solid coke or dust particles are separated together with the supplied solid particles via the cyclone separator from the gas stream, but the entire product gas stream must be passed through the separator. However, since no complete separation of all solid particles can be achieved in the cyclone separator, a process is used US 5186815 solid coke and dust particles with the product gas stream into downstream equipment parts, such as the cryogenic decomposition part, where they can lead to linings.

Of the The present invention is therefore based on the object, an alternative To develop a method for decoking a cracking furnace.

The This object is achieved in that the decoke exhaust via a cyclone separator fed back into the furnace of the cracking furnace or is led to a catalytic treatment, wherein the majority of solid particles in the cyclone is removed from the decoking exhaust gas.

at The process according to the invention becomes a decoking gas during a cleaning phase through the coking plant parts directed, wherein a decoking exhaust gas is formed. The resulting decoking exhaust gas contains mainly oxygen, nitrogen and water vapor Coke particles (dust particles), carbon monoxide and carbon dioxide. For the purposes of the invention, the decoke exhaust gas is the first on passed a cyclone. In such a cyclone separator For example, solid components can be separated from gaseous parts become. In Zyklonabscheider is therefore the predominant Part of solid particles (coke particles, dust particles) from the Decoking exhaust gas removed. The gaseous part of the decoking exhaust gas is in a suitable manner in the combustion chamber of the cyclone separator Slit furnace led, where at the prevailing temperatures Carbon monoxide almost completely converted to carbon dioxide is and a far-burning of the non-deposited coke particles he follows. Alternatively, the gaseous part of the decoking exhaust gas led from the cyclone separator to a catalytic treatment become. In the catalytic treatment (oxidation) becomes carbon monoxide converted to carbon dioxide. The decoke exhaust, as it ultimately leaves the cracking furnace or the catalytic treatment, is therefore almost free of solid particles such as coke particles and almost free of carbon monoxide. The invention Process thus provides an environmentally friendly alternative to decoking of cracking furnaces.

According to one preferred embodiment of the invention is water in the decoking exhaust gas injected in front of the cyclone separator. Through the injection of water in the decoking exhaust gas is the separation efficiency of the cyclone separator clearly improved. The emission of dust or coke particles can thus be further reduced. The solid particles of the decoking exhaust gas let yourself through the regular injection moisten with water, causing the separation of the solid particles is improved by the cyclone separator.

In another embodiment of the invention in a system with a furnace kiln consisting of several slit kilns become the decoke exhaust gases generated during the cleaning procedure conveniently over a single Cyclone separator for afterburning in the combustion chamber of a selected Slit furnace or in a catalytic treatment.

With In particular, the present invention succeeds in providing an alternative and to provide environmentally friendly methods of the prior art. With the aid of the present invention, both coke and dust emissions as well as the carbon monoxide content of the decoke exhaust before deflation minimized to the atmosphere.

in the The invention is based on a shown in the figure Embodiment explained in more detail become.

It demonstrate:

1 An embodiment of the invention with the return to the furnace of the cracking furnace and

2 an embodiment of the invention with a catalytic treatment.

1 shows a radiation zone ( 1a ) and convection zone ( 1b ) existing cracking furnace ( 1 ). During the decoking is in the crevices ( 2 ) and the subsequent split gas cooler ( 3 ) sent a mixture of air and water vapor. During decoking, the radiation zone ( 1a ) of the cracking furnace ( 1 ) over the burners ( 4 ) maintained at a temperature of about 1100 ° C. The decoke exhaust gas ( 5 ) becomes a cyclone separator ( 6 ). Before the cyclone separator ( 6 ), water ( 7 ) at regular intervals in the decoking exhaust gas ( 5 ) injected. In the cyclone separator ( 6 ) solid particles, such as coke particles or dust particles, are separated from the gaseous decoke exhaust gas ( 8th ). The decarburization off-gas released from solid constituents ( 9 ) is placed in the firebox of the radiation zone ( 1a ) of the cracking furnace ( 1 ) guided. At the prevailing temperatures in the decoking exhaust gas ( 9 ) remaining carbon monoxide almost completely converted to carbon dioxide. The, the cracking furnace escaping, exhaust gas ( 10 ) is thus now exempt from coke or dust particles and carbon monoxide.

The measured in this embodiment of the invention dust and carbon monoxide concentrations in the exhaust gas at the various positions (5, 9 and 10) are shown in the following table. Embodiment: position 5 9 10 Gas quantity [Nm ³ / h] 29,000 29,000 71,000 (including flue gas) Pressure [bar over atmosphere] 12:25 12:15 0 Temperature [° C] 450 450 180 Carbon monoxide * [ppmv] 1800 1800 <20 Dust (coke) * [mg / Nm ³ ] 1050 50 <20 * Mean over the decoking period

2 shows an embodiment of the invention with a catalytic treatment. The decoke exhaust gas ( 5 ) is transferred to a cyclone separator ( 6 ) after regular moistening ( 7 ), where from the decoking exhaust gas ( 5 ) solid components such as coke and dust particles ( 8th ) are separated out. The decarburization off-gas released from solid constituents ( 9 ) is converted into a catalytic treatment ( 11 ), where at temperatures dependent on the particular catalyst, carbon monoxide is oxidized to carbon dioxide and the remainder of the coke particles. The in the smoke outlet ( 10 ) guided exhaust stream is thus now freed from coke or dust particles and carbon monoxide.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 2830824 [0002]
• - DE 2854061 [0002]
• EP 0497155 [0006, 0006, 0007, 0009, 0009]
• - US 5186815 [0008, 0008, 0010, 0010]

Claims (3)

Process for decoking a cracking furnace ( 1 ) for the thermal cracking of hydrocarbons, in which a Entkokungsgas is passed through coked plant parts, wherein a decoke exhaust gas ( 5 ), characterized in that the decoke exhaust gas ( 5 ) via a cyclone separator ( 6 ) in the furnace of the cracking furnace ( 1 ) or to a catalytic treatment ( 11 ), whereby the majority of solid particles in the cyclone separator ( 6 ) is removed from the decoking exhaust gas. Process according to claim 1, characterized in that water ( 7 ) into the decoke exhaust gas ( 5 ) in front of the cyclone separator ( 6 ) is injected. Method according to claim 1 or 2, characterized in that the decoking off-gases ( 5 ) of several simultaneously decoked cracking furnaces ( 1 ) and via a cyclone separator ( 6 ) in the furnace of a cracking furnace ( 1 ) or in a catalytic treatment ( 11 ).