FR2588564A1 - Apparatus for cracking gaseous or liquid hydrocarbons - Google Patents

Abstract

Apparatus characterised in that it comprises: (a) a distributor connected to the feed block by a conduit, and to the upper entry orifices of the group of cracking reactors by entry pipes, the interior of these entry pipes being in communication with the free space between the outer and inner pipes of one of the reactors, (b) a manifold connected to a heat exchanger by an exit conduit, and to the upper exit orifices of the group of reactors by exit pipes, the interior of these pipes being in communication with the interior of the inner pipe of one of the reactors, (c) the invention relates to an apparatus for cracking gaseous or liquid hydrocarbons.

Description

"Apparatus for cracking (or cracking) hydrocarbons
gaseous or liquid
The invention relates to an apparatus for cracking (generally designated by the word cracking) gaseous or liquid hydrocarbons, so as to produce lighter olefins and, in particular, ethylene or other products used in industry. The apparatus is more particularly intended for the implementation of a process for pyrolysis of hydrocarbons carried out at a relatively high reaction temperature and for a very short contact time.

 The process for pyrolysis of gaseous or liquid hydrocarbons having a boiling point of 3600C, is generally implemented in the presence of dilution vapor in a pyrolysis oven where the suitable reaction chamber is constituted by one or more cracking reactors placed in the radiation chamber of the oven and heated by the thermal radiation of flameless burners. After leaving the cracking reactor, the gaseous reaction products, i.e. the pyrolysis gases, are cooled below the critical temperature of 6000C to avoid undesirable side reactions which would reduce the production yield of the product. The cooling takes place in heat exchangers in which the heat of the pyrolysis gases is used for the production of high pressure steam.

The unused gases pass from the radiation chamber to a convection section where their residual heat is used to preheat the feed raw material, the dilution vapor, the combustion air, the feed water to the heat exchangers. high pressure heat, and to superheat the high pressure steam produced in these exchangers.

 Cracking reactors are generally produced in the form of helical tubes placed in a vertical or horizontal position inside the radiation chamber of the pyrolysis oven. The apparatus of this type allows pyrolysis to be carried out at a temperature of 700 to 8000C for a contact time of 0.3 to 1.0 seconds. It is also known devices in which the pyrolysis oven contains a group of straight tubes of relatively small diameter located in a vertical position inside the radiation chamber of the pyrolysis oven and provided with lower inlet openings and upper outlet ports. A device of this type makes it possible to carry out what is called a millisecond pyrolysis in which the reaction proper takes place during a contact time of less than 0.3 seconds and at a relatively high temperature influencing favorably the quality of the product and its production yield.

 In another known device, millisecond pyrolysis is carried out in pyrolysis ovens containing at least one group of pyrolysis reactors with two elongated pipes provided with upper inlet ports and upper outlet ports.

Each reactor consists of an outer pipe and an inner pipe directed coaxially downwards inside the outer pipe, a certain clearance is provided between the inner surface of the outer pipe and the outer surface of the inner pipe. Towards the open lower end of the interior pipe is mounted a partition wall provided with a semiannular groove, this partition closing the outside pipe from below and reversing the downward flow of hydrocarbons passing from the inlet in the inner pipe, to transform it into an upward current going towards the exit orifice by pissing through the free space formed between the outside pipe and the inside pipe. The upper part of each cracking reactor leaves the pyrolysis oven and is located surrounded by a two-pipe heat exchanger serving as a block for preheating the feed material and, at the same time, for cooling the pyrolysis gases.

 The advantage of this arrangement is that the part of the cracking reactor which is located in the radiation chamber has a low height, and that it is possible to use the heat transfer between the updraft and the downdraft of hydrocarbons in addition to the heat produced by flameless burners. On the other hand, the upper part of the cracking reactor serving as a heat exchanger is relatively complicated and has a relatively large height. In addition, the development of the heating of the treated material is not satisfactory, since it is less intense in the first phase of the reaction than in the other. Also because of this, the distribution of temperatures at the surface of the various parts of the reactor is not favorable and reduces the life of the device.

 The object of the invention is to use the favorable characteristics of known double-pipe cracking reactors while avoiding their drawbacks indicated above.

 To this end, the invention relates to an apparatus for cracking hydrocarbons, gaseous or liquid, comprising a pyrolysis oven containing at least one group of cracking reactors with double elongated vertical pipes, a power supply unit for cracking reactors steam and hydrocarbons or a mixture of hydrocarbons, and means comprising at least one heat exchanger for cooling the hot pyrolysis gases after they have left the cracking reactors, each cracking reactor being constituted by an external pipe and an inner pipe and having an upper inlet port connected to the power supply and an upper outlet port connected to the cooling block, the inner pipe having an open lower end and extending coaxially downwardly therein of the outer pipe, with a free space provided between the inner surface of the outer pipe and the outer surface of the inner pipe, means being used for r close the outer pipe from below and to reverse the downward flow of hydrocarbons in the cracking reactor so as to transform it into an upward flow, piping means being used to connect the inlet ports of the cracking reactors to the power supply unit and the outlet orifices of these cracking reactors to the cooling means, apparatus characterized in that the piping means comprise a) at least one distributor connected to the power supply unit by at least one supply line, and to the upper inlet ports of at least one group of cracking reactors by a number of inlet pipes, the interior of each of these inlet pipes being in communication with the free space provided between the pipe outside and the inner pipe of one of the cracking reactors, b) at least one manifold connected to at least one heat exchanger by at least one outlet pipe, and to the upper outlet ports d at least one group of cracking reactors through a number of outlet pipes, the interior of each of these outlet pipes being in communication with the interior of the inner pipe of one of the cracking reactors.

 In different embodiments of the invention, the outer pipes are aligned vertically with the inner pipes; the inlet pipes are fixed tangentially to the periphery of the outside pipes; transverse blades are mounted in the free spaces between the outer pipes and the inner pipes, these blades being preferably arranged in a helix; and some of the inlet pipes are fitted with throttle valves or their internal diameter is reduced compared to that of other inlet pipes.

 In the apparatus according to the invention, since the feed raw material is brought into the free space provided between the outer pipe and the inner pipe, better conditions are offered for transferring heat to the treated material and for obtaining a soaking reaction in the inner pipe before cooling of the pyrolysis gases in the high pressure heat exchanger. Good conditions are also created for vaporizing and praying; heating the raw material of hydrocarbons entering into reaction. Other advantages are constituted by a very short contact time of the feedstock in the cracking reactors, a low pressure drop, a high cracking rigor, and a long service life resulting from a deposit of coke. very weak in the pipes. The structure of the device is relatively simple, the necessary costs of investment and raw material are lower. The favorable distribution of temperatures on the surface of the various parts of the cracking reactors makes it possible to guarantee a relatively long service life of the apparatus.

 The general arrangement of the device according to the invention is not very different from that of a conventional device. As a result, it is possible to apply the invention to the overhaul and modernization of existing installations without the need to modify their support structure, their convection section and their cooling section.

The invention will be described in more detail below, by way of examples, with reference to the accompanying drawings in which
- Figure 1 is a schematic side view illustrating an apparatus provided with a group of cracking reactors
- Figure 2 is a front view of the same device
- Figure 3 is a longitudinal sectional view illustrating a cracking reactor to which the associated piping elements are connected
- Figure 4 is a sectional view of the cracking reactor along line II of Figure 3;
- Figure 5 is a sectional view of the cracking reactor along line II-II of Figure 3; and
- Figure 6 is a schematic front view illustrating an apparatus with four groups of cracking reactors.

As indicated in FIGS. 1 and 2, the apparatus according to the invention comprises a group 20 of cracking reactors 2 arranged on a single line inside a radiation chamber 32 of a pyrolysis oven 1. The radiation chamber 32 is equipped with flameless burners (not shown), and the interior
laughter of this room is connected inside a
convection section 27. As shown in the figures
3, 4 and 5, each cracking reactor 2 is made up
an outer pipe 3 and an inner pipe 4 descending coaxially inside the outer pipe 3 and having an open lower end 8. Between
the inner surface of the outer pipe 3 and the outer surface of the inner pipe 4 is a free space in which transverse blades 9 are arranged in a helix.

 The free space between the pipes is closed on top by an upper cover 7. The lower part of the free space is connected to a free chamber located under the open end 8 of the inner pipe 4 opposite which is placed a partition 5 provided with a semi-circular groove 6, which makes it possible to close the interior of the external pipe 3 from below. Each cracking reactor 2 has an upper inlet orifice 10 and an upper outlet orifice 11.

The inlet 10 of the cracking reactor 2 is located in the vicinity of the upper cover 7 and is connected to the end of an inlet pipe 13 fixed tangentially to the periphery of the outer pipe 3. The inlet pipe
13 is curved to compensate for the effects of the dilata
thermal tion. The outlet 11 of the cracking reactor 2
is located in the center of the top cover 7 between the pipe
inside 4 and an outlet pipe 12 vertically aligned with the inside pipe 4 and forming an integral part
of it.

All inlet pipes 13 are
connected to a distributor 14 in the form of a horizontal tube connected, by a single supply line 15, to a pipe passing through the convection section 27 and connected to a unit (not shown) for supplying material to treat. All the outlet pipes 12 are connected to a manifold 16 in the form of a horizontal tube and connected, by a single outlet pipe 17, to the lower part of a heat exchanger 18 constituting the essential part of a cracking section 26. The upper part of the heat exchanger 18 is provided with an outlet pipe 23. The heat exchanger 16 is, moreover, connected, by a down pipe 24 and an up pipe 25, to a steam separator tank 19 provided with a water hose 21 and a steam pipe 22.

 Referring now to Figure 1, there is now described a pyrolysis process implemented in the apparatus according to the invention. The feed raw material, that is to say the hydrocarbons, is sent to the convection section 27 where it is preheated by the unused gases 28 coming from the radiation chamber 32. After having been mixed with the steam dilution 31, the raw material is preheated again in the convection section 27. Then the mixture passes through the supply line 15 to enter the distributor 14 which it then leaves to pass through the inlet pipes 13 and enter the cracking reactors 2. In the cracking reactor 2, the mixture flows downwards, from the inlet orifice 10, passing into the free space formed between the outer pipe laugher 3 and the inner pipe 4 to reach the partition 5, then, after being reversed in the opposite direction by the semi-annular groove 6, the mixture rises in the form of pyrolysis gas passing inside the inner pipe 4 to reach the outlet 11.

 During the passage of the mixture in the free space provided between the external pipe 3 and the internal pipe 4, the cracking of the hydrocarbons takes place under the action of the heat of the radiation chamber 27 transmitted to the mixture through wall of the outer pipe 3, and under the action of the heat of the hot pyrolysis gases transmitted through the wall of the inner pipe 4. The intensity of the heat transfer is increased by the turbulence of the mixture caused by the tangential entry of the mixture in the cracking reactor 2 and by contact of the mixture with the blades 9. The pyrolysis gases are first precooled in the interior pipes 4 where they transmit their heat to the mixture passing through the free spaces between the outside pipes 3 and inside pipes 4, then, in the outlet pipes 12 where they transmit their heat to the open air.

 After entering the manifold 16, the pyrolysis gases are sent, via the outlet pipe 17, into the heat exchanger 18 where they are cooled by a mixture of steam and water brought into the heat exchanger 18 by the down pipe 24 connected to the water-steam separation tank 19 supplied with water 29 preheated in the convection section 27. The high pressure steam 34 produced in the heat exchanger 18 passes through the up pipe 25 to enter the tank of water-vapor separation 19 from which it is discharged by the steam pipe 22. The cooled pyrolysis gases are discharged from the heat exchanger 18 in the form of a finished product 33 leaving through the outlet pipe 23.

 The apparatus represented in FIG. 6 comprises four groups 20 of cracking reactors 2 placed in a radiation chamber 32 of the pyrolysis oven 1, four distributors 14, two collectors 16 and two heat exchangers 18. Each group 20 of cracking reactors 2 is supplied with a mixture of hydrocarbons and steam by a separate supply line 15 and by a separate distributor 14, each of the two manifolds 16 being connected to a pair of groups 20 of cracking reactors. Each collector 16 is connected by a separate outlet pipe 17 to one of the two heat exchangers 18 both connected to a single water-vapor separation tank 19.

 As the pressure of the mixture passing through the distributor 14 decreases in proportion to the distance separating it from the mouth of the supply line 15, an uneven supply of the pyrolysis reactors 2 could occur. The same effect could be produced by the deposition of coke in the cracking reactors 2. This uneven supply can be avoided by throttling the flow of the mixture in some of the inlet pipes 13, for example by mounting throttle valves in the inlet pipes 13 or by reducing their diameter.

 The examples below illustrate the invention without affecting the generality of the characteristics defined elsewhere here.

EXAMPLE 1
A device model has been built and tested. In this model, the pyrolysis reactor consisted of an outer pipe having a diameter of 57 X 5 mm and an inner pipe having a diameter of 30 x 3 mm. The two pipes were approximately 6,000 mm long.

Parameters of the pyrolysis process
Maximum raw material supply .... 100 Kg / hour
Steam supply 0.5 to 0.7 times the
raw material
Mixing temperature at the inlet. . . . 500 to 650 C
Temperature of the mixture in the inversion zone 820 to 9200C
Production yields .... 11 to 13% by weight of CH4
25 to 34% by weight of C2H4
14 to 17% by weight of C 3H4
Naphtha raw material
Contact time 0.1 second
EXAMPLE 2
An apparatus comprising 32 pyrolysis reactors and having a capacity of 11,200 kg / hour was used. The inside diameter of the outside pipes was 102 mm and the inside diameter of the inside pipes was 60 mm. The length of the pipes in the radiation chamber was 10 meters.

Parameters of the pyrolysis process
Naphtha raw material
Raw material distillation range 50 to 1700C
Raw material flow rate through a cracking reactor 350 Kg / hour
Raw material flow rate through the radiation chamber 11,200 Kg / hour
Steam flow through a cracking reactor 175 Kg / hour
Steam flow through the radiation chamber 5 600 Kg / hour
Pyrolysis control temperature.

8800C
Raw material temperature at the entrance to the convection section ....

600C
Mixing temperature at the outlet of the convection section 6200C
Pyrolysis gas temperature at the outlet of the heat exchanger 350 to 4500C
Temperature of unused gases on the fire deck of the radiation chamber. 1.1000C
Temperature of gases not used in column 1900C
Methane fuel gas
Temperature of pyrolysis gases at the outlet of the 8000C cracking reactor
Fuel consumption 1,380 Kg / hour
Thermal output power of the 19.1 MW pyrolysis oven
Heat consumption of the radiation chamber â, 4 ME

Claims (6)

CLAIMS 1) Apparatus for cracking hydrocarbons, gaseous or liquid, comprising a pyrolysis oven containing at least one group of cracking reactors with double elongated vertical pipes, a power supply unit for cracking reactors in steam and hydrocarbons or mixed with hydrocarbons, and means comprising at least one heat exchanger for cooling the hot pyrolysis gases after they have left the cracking reactors, each cracking reactor consisting of an external pipe and an internal pipe and comprising an upper inlet port connected to the power supply unit and an upper outlet port connected to the cooling unit, the inner pipe having an open lower end and extending coaxially downward inside the outer pipe, with a free space between the inner surface of the outer pipe and the outer surface of the inner pipe, means being used to close the pipe ex bottom and to reverse the downward flow of hydrocarbons in the cracking reactor so as to transform it into an upward flow, piping means being used to connect the inlet ports of the cracking reactors to the power supply and the outlet orifices of these cracking reactors to the cooling means, apparatus characterized in that the piping means comprise (a) at least one distributor connected to the supply unit by at least one supply line, and to the orifices upper inlet of at least one group of cracking reactors by a number of inlet pipes, the interior of each of these inlet pipes being in communication with the free space provided between the outer pipe and the inner pipe of one of the cracking reactors, (b) at least one manifold connected to at least one heat exchanger by at least one outlet pipe, and to the upper outlet ports of at least one group cracking reactors by a number of outlet pipes, the interior of each of these outlet pipes being in communication with the inside of the inner pipe of the cracking reactor nb.  20) Apparatus according to claim 1, characterized in that the outlet pipes are aligned vertically with the inner pipes.  30) Apparatus according to any one of claims 1 and 2, characterized in that the inlet pipes are fixed tangentially to the periphery of the outer pipes.  40) Apparatus according to any one of claims 1 to 3, characterized in that transverse blades are placed in the free spaces formed between the outer pipes and the inner pipes.  50) Apparatus according to claim 4, characterized in that the transverse blades are arranged in a helix.  60) Apparatus according to any one of claims 1 to 5, ~ characterized in that some of the inlet pipes are provided with throttling means.  7) Apparatus according to claim 6, characterized in that some of the inlet pipes are provided with throttle valves.  80) Apparatus according to claim 6, characterized in that some of the inlet pipes have a reduced internal diameter.