Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By c content reduction – e.g. – cracking – etc.
Patent
1990-12-12
1993-01-05
McFarlane, Anthony
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By c content reduction, e.g., cracking, etc.
134 7, 134 8, 134 2211, C07C 404, B08B 904
Patent
active
051772922
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of steam cracking hydrocarbons, the method serving in particular to avoid or at least limit coking in the steam cracking installation.
The steam cracking of hydrocarbons consists in subjecting a feedstock of hydrocarbons mixed with steam to thermal cracking in an installation comprising, in particular, a furnace having tubes in which the feedstock is raised to a temperature of about 800.degree. C. to 900.degree. C., followed by indirect quench means for the gaseous effluent leaving the furnace, enabling the effluent to be cooled quickly in order to stop the cracking reactions.
The main drawback of this method lies in the installation becoming progressively caked with coke which is deposited in the furnace and in the indirect quench means.
A layer of coke whose thickness increases progressively is formed on the inside walls of the installation that come into contact with the feedstock to be cracked, and this layer is objectionable from the point of view of heat transfer and it also leads to an increase in the head losses inside the tubes of the furnace, and to a drop in yield.
It is therefore necessary from time to time to eliminate the coke that is deposited in such installations.
Proposals have already been made to do this by a chemical decoking method based on oxidization using an air-steam mixture. However, implementing this method requires the operation of the steam cracking installation to be interrupted and the equipment situated downstream to be isolated.
Proposals have also been made to decoke the indirect quench means by hydraulic sand blasting or by means of jets of water under very high pressure, thereby breaking up the layer of coke. Here again, it is necessary to interrupt the operation of the steam cracking installation completely.
Proposals have also been made to decoke by methods which consist essentially in injecting solid particles into the steam cracking installation. A first method consists in causing a flow of inert gas to flow while conveying metal particles of relatively large size (250 .mu.m to 2,500 .mu.m) through the furnace after it has been connected to the atmosphere. Another method proposes continuously sand blasting the steam cracking installation by injecting sand into the liquid hydrocarbon feedstock. The particles of sand pass through the steam cracking furnace and the indirect quench means and they are finally trapped by the heavy oil used for direct quenching of gaseous effluents. Since the mean diameter of sand particles is generally about 1 mm, this gives rise to significant erosion in the tubes conveying the feedstock and the steam cracking effluents. In addition, it is almost impossible to separate the particles of sand from the direct quenching heavy oil economically, and as a result the particles of sand cannot be recycled and the quenching oil becomes unuseable.
This means that the prior methods of steam cracking hydrocarbons are performed discontinuously, with periods of hydrocarbon steam cracking alternating with intervals during which the installations are decoked, thereby reducing yields and increasing costs.
A specific object of the invention is to provide a method of steam cracking hydrocarbons which is capable of being performed continuously over very long periods of time without it being necessary to stop steam cracking in order to decoke the corresponding installation.
Another object of the invention is to provide a method of this type enabling the formation of coke in the installation to be prevented or at least very greatly limited, without any risk of damaging the components of the installation.
To this end, the invention provides a method of steam cracking hydrocarbons, the method consisting in causing steam and hydrocarbon feedstock to flow high speed through an installation comprising at least one steam cracking furnace having tubes and indirect quench means for the gaseous effluents leaving the furnace, and in injecting erosive solid particles into the installation, with the particles being conveyed by a flow of ga
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patent: 4482392 (1984-11-01), Pollock et al.
patent: 4572744 (1986-07-01), Dominick
patent: 4579596 (1986-04-01), Murzyn
McFarlane Anthony
Procedes Petroliers et Petrochimiques
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