Steam cracking process and facility comprising injection of powd

Details Steam cracking process and facility comprising injection of powd Steam cracking process and facility comprising injection of powd

1997-06-25

1998-10-13

Yildirim, Bekir L.

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Cracking

208126, 208131, 208132, 208 48R, 208 48AA, 208 48Q, 208151, 208152, 208161, 208168, 208174, 208175, 208176, 422144, 422145, 422146, 422147, 422200, 422213, 422214, C10G 936, C10G 918, B01J 808

Patent

active

058207473

DESCRIPTION:

BRIEF SUMMARY
Steam cracking is the basic process in petrochemistry. It consists of thermally cracking a mixture of hydrocarbons and steam at high temperatures of the order of 850.degree. C. then chilling the effluents in an indirect chilling exchanger generally designated by TLX or TLE (transfer line exchanger) then fractionating the cooled effluents.
The main operating problem in this process is caused by unwanted deposits of coke in the pyrolysis tubes and in the transfer line exchanger.
In order to limit or overcome this problem, a steam cracking process has been proposed which involves injection of solid erosive particles (powder) to eliminate at least a portion of the coke deposits. The particles are injected "in line", i.e., either during the normal steam cracking operation, or during phases when the supply of hydrocarbons is temporarily and briefly stopped (normally for a period of less than two hours), the furnaces being flushed by steam alone, and remaining connected to the downstream sections for the treatment of the cracked gases. The preferred operating mode consists of injecting the particles during normal operation of the furnace, optionally temporarily increasing the volume flow rate of the cracked gases at the moment of injection of the powder, to increase the effectiveness.
In general, and particularly when mineral or metallic particles are injected, which do not essentially consist of coke, it is necessary to separate the injected powder at the outlet from the transfer line exchangers, in order not to pollute the downstream sections for treatment of the cracked gases. The recovered powder must then be stored either for evacuation if the process operates without recycling, or for recycling, at least in part.
A typical steam cracking facility has a plurality of furnaces, each generally having several transfer line exchangers (TLE) for the effluents; for example, there may be ten furnaces each with two TLEs, giving a total of 20 TLEs operating in parallel.
For reasons of cost and maintenance, it is preferable for there to be only a very limited number of drums for receiving and storing the recovered powder (used powder) and/or any equipment for its treatment before recycling.
The number of drums for receiving and/or the number of modules for treating the recovered powder for recycling may, for example, be limited to a maximum of two.
Preferably, if possible a single module for receiving and/or treating recovered powder is chosen, which is common to the whole steam cracking facility.
In a first variation of the described process, all the effluents from the different TLEs are collected. This is generally carried out in a conventional steam cracking facility without injection of erosive powder, and the powder is separated from the totality of the effluent from the steam cracking facility to recover this powder at a single point. This involves the installation of a very high capacity cyclone which is difficult and costly to install, to treat the entirety of the steam cracking effluents, and also to transport solid particles in the totality of the circuits for collecting the cracked gases.
This technical solution is costly and has risks associated with possible erosion of the numerous bends in the collection circuits; in addition, the efficiency of a very large cyclone is very mediocre.
In a further variation of the steam cracking process involving injection of erosive powder and recovery thereof at a single point, doses of powder are sequentially injected into different points in the facility, for example successively upstream of the different TLEs and/or coils in the pyrolysis tubes and, coordinated with the powder injection, sequentially directing the different effluents charged with the particles to a single gas/solid separation module.
As an example, the effluents from each TLE can be sequentially directed, at the corresponding moment of injection of the powder upstream of the TLE under consideration, to a single cyclone to recover particles transported by the cracked gases (injected powder and eroded co

REFERENCES:
patent: 5183642 (1993-02-01), Lenglet

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