DE1118912B - Continuous use of coke as a heat carrier in continuously operating cracking processes - Google Patents

Description

Continuous use of coke as heat transfer medium in continuously operating cracking processes In a known continuously operating cracking process, as described in German patent 974535 , in which, in addition to the production of liquid and gaseous products, the extraction of petroleum coke is an essential part of the process The oil to be split is placed on pre-grained coke (mother coke) that has been transported and heated by various methods. While the gaseous products are discharged in the usual way, the mother coke, on which new coke layers build up in the course of the reaction, remains in the cracking plant. In the processes known up to now, it was discharged to the extent that it was newly formed. As a result, the amount of coke, which is constantly increasing during cracking, is kept in its entirety at the normal level limited by the size of the apparatus. Practice has now shown that the problem of the continuous recovery of petroleum coke formed during the process is technically and economically unsatisfactory.

This shows, for example, that it is necessary to use the splitting system to constantly withdraw the mother coke (mixed coke) that has grown too strong with petroleum coke, to prevent clogging of the coke fluidized bed. The one permitted in the system The largest cross-section of the mixed coke is a function of the pipe cross-sections of the coke fluidized bed and the performance of the conveyor system, especially with pneumatic conveyance. At the same time, in order to maintain the continuity of operations, it is necessary the coking cycle of mother coke of a certain maximum grain size again and again to feed.

It has already been proposed to discharge mixed coke and replace it a corresponding amount of mother coke for the mixed coke discharged, the but consists of newly formed particles to be reintroduced into the apparatus. These The addition of newly produced heat transfer particles is technically extraordinary unsatisfactory.

It has now been found that coke particles (pellets, pebbles) as Heat transfer medium in cracking processes in which more coke is deposited on the shaped heat transfer medium arises, can thus be used continuously and the economically valuable can also continuously win coke formed in the course of the reaction, that in the course of the cracking process evenly grown heat transfer media appropriate point from the continuous process, by appropriate, in itself known mechanical measures freed from the grown coke layer, the resulting Separates products using known measures and continuously feeds them back into the cracking process.

It is advantageous that the method according to the invention can be carried out can, since the once used and in its production in the specified way expensive mother coke can continue to be used. It was unpredictable that by means of measures known per se, such as moderate pressure or impact (the is exercised, for example, by commercially available roll crushers or ball mills), the mixed coke in re-usable mother coke and in the course of the process "Grown" shell coke can be separated. For example, you can proceed like this that the roller spacing of a roller crusher loaded with mixed coke is set in such a way that that it is only slightly larger than the largest diameter of the mother coke. Here the mixed coke to be broken down is expediently applied in one layer thickness the roll crusher, which corresponds to the diameter of the mixed coke. In this way the shell coke can be removed practically without breaking up the mother coke. Of the Mixed coke unexpectedly holds the stress of pneumatic conveying off, on the other hand, through the entire mechanical measure in mother coke and shell coke split.

Another advantage of the claimed method over a indiscriminate crushing of the mixed coke without separating the shell coke from the mother coke - lies in it; that the good flow properties, given by the regular geometric The shape and size of the mother coke retained when it was used as a heat transfer medium stay. This is important when the heat transfer medium, only by gravity moved at the highest possible speed through pipe systems have to. The mixed coke would be broken indiscriminately and / or a separation of the If there are no shells, then there would be too many due to the accumulation of heat carriers rough and geometrically irregular surfaces and / or too small a particle size to technically intolerable stagnation in the flow of heat transfer media.

One can get the following idea regarding the origin and of the behavior of the mixed and shell coke: The mother coke used coats during the cracking process more or less quickly, depending on the size of the used Particles and the type of feed oil, with a shell of petroleum coke (shell coke). It has been found that mother coke with a mean diameter of, for example about 9 mm, shell coke in a thickness of 3 mm and more in a fairly uniform Shift begins; the weight of the shell coke is at least equal in this case the weight of the mother coke. It was also found that mother coke and shell coke, although both are made of petroleum coke, due to their different origins show a significantly different behavior towards mechanical loads. So, as long as they are thin, coke shells adhere very firmly to the mother coke. As soon but a certain layer thickness is reached (about 1 mm), the connection is made with the mother coke looser. This loosening of the coke shells on the mother coke will favored by rapid temperature fluctuations. Such processes play out in the process according to German patent 974 535.

The inventive method can be carried out as follows: The The mixed coke to be broken is branched off from the coke circuit of the cracking plant continually. Mixed coke with a diameter of, for example, 13 mm has exceeded, with the help of sieves, preferably grate sieves, in the separation vessel at the peak of the pneumatic conveying or at the same point by air separation or by a combination of sieving and air sifting or another physical one Separation method can be deducted.

But you can also add the coke in proportion to the increase in volume of the coke filling can only be removed from the system in a partial flow if, after passing the Separation vessel is already in the downward part of the coke circuit located above the coke heater, and then a separation of up to one Make certain size grown mixed coke with the above tools. The structure of the mixed coke can be seen in Fig. 3. In Fig.4 is broken up Mixed coke shown. .

It is advantageous if the coke is in a place of the lowest temperature is branched off from the coke circuit of the cracking plant. Furthermore, this extraction point should lie so that the coke after leaving the oil injection zone 8 (see Fig. 1 or 2) an optimal period of time for »consolidation of the structure« (»fermentation«) remains, so as not to impair its economic usability.

That which arises after the shell coke has been blown off the mother coke loose mixture of the two components is made by physical-technical methods, such as sieving or air sifting, separately, with of course also optionally existing dust particles are removed. The shell coke is diverted as production, and the mother coke and possibly also larger fragments of shell coke as a heat transfer medium or crystallization nuclei for the petroleum coke produced smuggled into the cracking plant. This infiltration can either be above the Koksaufheizers 6 or below the reactor 7 or at the lower end of the pneumatic Conveyor line (see Fig. 1 or 2).

The method according to the invention can be particularly advantageous apply the procedure of patent 974,535.

Examples of the application of this continuously operating process are given in Figs. 1 and 2.

Example 1 (to Fig. 1) In the separating vessel 1 belonging to the coke circuit A, mixed coke> 12 mm is separated from the coke circuit A with the aid of grate screens and fed to the roller crusher 3. This coke stream can be passed through the heat exchanger 2 in order to reduce the thermal stress on the roll crusher. After passing the roller crusher, the loose mixture of mother coke and shell coke is separated by air sifting, the shell coke is removed from the system and the mother coke (mainly particles of about 9 mm in diameter) is fed back to the coke circuit A via the lift pot 9 via the intermediate vessel 5. Example 2 (to Fig.2) According to the coke formation in the course of the cracking, the coke level rises in the intermediate container 1 belonging to the coke circuit A. When a certain level is exceeded, coke flows from there - possibly via the heat exchanger 2 - to the roller crusher 3, the roller spacing of which is set to 10 mm. Mixed coke> 10 mm is broken down into mother coke (diameter approx. 9 mm) and shell coke; Mixed coke <10 mm passes the roller crusher unchanged. In sifting 4, the shell coke is removed from the plant and the mother coke and unchanged mixed coke are reintroduced into the coke circuit A upstream of the coke heater.

Claims (1)

PATENT CLAIM: A process for the continuous use of coke particles as a heat carrier in continuous-working cracking process, the heat transfer plate in which in the course of the process, with a layer of coke, characterized in that one removes the evolved during the cracking process the heat carrier at a suitable location of the continuous process, the The coke layer is removed from the heat transfer medium by suitable mechanical measures known per se, the resulting products are separated by known measures and the heat transfer medium is continuously fed back into the continuous process.