US3408417A - Thermal cracking method of hydrocarbons - Google Patents

Description

Oct. 29, 1968 TORU SOGAWA ET AL THERMAL CRACKING METHOD OF HYDROCARBONS Filed Aug. 20, 1965 m wm 5 6 8 9 In! 7 1H! m l u FIG. 2

INVENTORS Tonu SOG'AW Tosmo HANM Sumvm GoM BY wmqsawiwwlcmf United States Patent 015cc 3,408,417 Patented Oct. 29, 1968 I 3,408,417 1 THERMAL CRACKING METHOD OF HYDROCARBONS Toru Sogawa, Ichikawa-shi, Shinpei Gomi, Nakoso-shl, and Toshio Kauai, Ota-ku, Tokyo, Japan, assignors to Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan Filed Aug. 20, 1965, Ser. No. 481,281 Claims priority, application Japan, Aug. 24, 1964, 39/ 47,125 6 Claims. (Cl. 260--679) ABSTRACT OF THE DISCLOSURE Method for thermal cracking of hydrocarbons including introducing combusting gases and hydrocarbons into a first zone, the latter at a speed of sound or greater, then passing the thereby mixed resultant through a constriction at thefspeed of sound or greater into a second zone for thermal cracking purposes, then quenching the reactants with a coolant.

The present invention relates to a process for the thermal cracking of hydrocarbons.

When unsaturated hydrocarbons such as acetylene and ethylene are produced by industrial thermal cracking of hydrocarbons, it is quite important to produce acetylene and ethylene in a good yield. It is necessary, furthermore, that a stabilized thermal cracking reaction and stabilized formation of the product gas are attained by inhibiting formation of carbon and tar during the thermal cracking reaction of the hydrocarbons to prevent clogging of the thermal cracking furnace and to enable a continuous Operation of the furnace, and by minimizing the variations in the yield of acetylene and ethylene and also in the pro duction ratio of the above two products.

The present invention is based upon the discovery that if the flow velocities to be adopted for the injection of the raw material hydrocarbons from the injection nozzle and for the flow of the mixed fluid containing said hydrocarbons and combustion gas at a high temperature at the throat passage of the furnace are respectively kept at the velocity of sound or at a velocity of more than the velocity of sound, a constant flow rate of the every fluid can be accordingly attained with the maintaiuance of stable ratio of formation of either products, and furthermore, the'formation of carbon and tar is thereby suppressed. In the specification and claims, the velocity of sound means the velocity of sound which is defined by the pressure, temperature and gas composition under the flowing condition of the fluid.

The: present invention is a process for the thermal cracking of hydrocarbons characterized in that in an apparatus consisting of a burner, a combustion chamber, a throat passage, a thermal cracking reaction chamber and a quencher. Fuel and oxygen are combusted in the combustion chamber by means of the burner, the formed high temperature combustion gas is mixed with hydrocarbon or a mixed fluid of hydrocarbon and hydrogen and/or 'steam by injecting the latter into the former from a nozzle provided on the upper part of throat passage at the velocity of sound or at a velocity more than the velocity of sound and then a mixed fluid thus obtained is injected into the thermal cracking reaction chamber through the throat passage at the velocity of sound or at a velocity more than the velocity of sound to thermally crack the hydrocarbon. The process of the present invention will now be more fully described with reference to the accompanying drawings. It is to be understood that such description is included merely by way of illustration and is in no way intended to limit the scope of the invention.

In the drawings:

FIGURE 1 shows a vertical section of furnace which is suitable for the practice of process of present invention, and

FIGURE 2 shows a graph in which the results obtained by the process of the present invention are compared with the results obtained by the process of the prior art.

In FIGURE 1, a fuel is introduced from a nozzle 1 and simultaneously oxygen and steam are introduced from a nozzle 2. The fuel, oxygen and steam are injected into a combustion chamber 6 from a burner 5 to burn the fuel and to form a combustion gas of high temperature. The hydrocarbon as the raw material to be injected into the combustion gas for the cracking is preheated and is introduced from a nozzle 3 and injected from an injection nozzle 7 into the combustion chamber 6 at the velocity of sound or a velocity more than the velocity of sound and is admixed with the combustion gas of high temperature. When the raw material for cracking is injected into the comustion chamber at the velocity of sound, a constant flow rate of the raw material to be injected into the combustion chamber can be attained without trouble caused by the deviation of pressure in the combustion chamber, and a rapid and uniform mixing of the raw material for cracking with the combustion gas of high temperature can be achieved. Consequently a formation of carbon and tar is low and deposition onto furnace wall of carbon and tar does not occur and thus favourable reaction results can be obtained. If the flow velocity does not reach the velocity of sound with the sole introduction of the cracking raw material, the admixing of hydrogen or steam with said cracking raw material is recommended, thereby the flow velocity is maintained at a velocity more than the velocity of sound and thus an identical effect with the case of sole introduction of the cracking raw material at the velocity of sound or at a velocity more than the velocity of sound can be obtained, especially an increased yield can be achieved in the case of the using of hydrogen. The mixed fluid which is the cracking raw material admixed with the combustion gas at high temperature is introduced into the bottom part of the combustion chamber with a flow velocity less than the velocity of sound, it is jetted into the reaction chamber 9 through the throat passage 8 at the velocity of sound or at a velocity more than the velocity of sound velocity and there the cracking reaction is carried out. After the cracking reaction, the products are rapidly cooled by means of cooling water which is introduced into the terminal position of the reaction chamber through the pipe 4 and thereby terminating the reaction. The reaction products was withdrawn from the pipe 10.

When the flow velocity at the throat passage 8 is maintained at the velocity of sound or a velocity more than the velocity of sound, the admixing of the raw material for cracking with the combustion gas at high temperature is rapidly and uniformly carried out and at the same time the turbulence in the combustion chamber of the admixed gas does not occur and thus uniform combustion can be carried out. As a result, a uniform mixed fluid of the raw material for cracking and the combustion gas at high temperature can be flowed from the combustion chamber to the reaction chamber and thus a cracking reaction can be carried out at a uniform reaction temperature. Therefore, the increase of yield results. which are obtained by maintaining-the flow velocity of the raw material for cracking and the flow velocity results obtained are shown in the following table comparing the results of example.

TABLE Method Comparative methods Experiment Number Unit of this invention 1 2 3 Flow velocity of raw material Mach (M) I 1.0 ,0.4. 1.0 0.4

for cracking.

Flow velocity at throat passa e do 1. 1. 0 0. 4 0. 4 Acetylene... Wt. percent 23.6 4 23.4 21.3 r 20.8 Ethylene do. 35.3 30.5 I 31.3 20.3 Acetylene plus ethylene do 58. 9 53. 0 52. 6 50. 1 Carbon balance..-..'....';.' do 98.2 95.8 95.1 92.1 Carbon deposit of the furnace None (L interior.

l Little deposit around the injection nozzle and the throat passage;

2 Deposit onto the wall of reaction chamber.

at the throat passage of the admixed fluid at the velocity of sound velocity or at a velocity more than the velocity of sound are as described above. When only one of these procedures is carried out, however, the increase of yield of acetylene and ethylene which are the desired products and the elimination of variation of the ratio of the both products and the suppression of formation of carbon and tar are not attainable. Therefore the success of the purpose can be achieved only by the simultaneous use of both procedures. When the flow velocity at the throat passage is less than the velocity of sound even if the raw material for cracking is constantly injected into and mixed with the combustion gas of high temperature at the velocity of sound or at a velocity more than the velocity of sound, the combustion in the combustion chamber becomes ununiform and the compositon of high temperature combustion gas is changed and as a result mixing of the raw material for cracking with the combustion gas becomes nonuniform, and thus a rapid mixing is not attained and the decrease of yield of acetylene and ethylene and the variation of the ratio of both products and the formation of carbon and tar on the wall of the reaction chamber occur. When the raw material for cracking is not injected at the velocity of sound or a velocity more than the velocity of sound even if a high temperature combustion gas is formed by effecting uniform combustion with the flow velocity at the throat passage of more than at the velocity of sound or a velocity more than the velocity of sound, it is diflicult to inject the raw material for cracking into the reaction chamber and as a result the mixed fluid of the raw material for cracking and the high temperature combustion gas becomes nonuniform, and further carbon and tar are deposited on the wall of the throat passage part and the yield of acetylene and ethylene are decreased and thus the ratio of the both products is changed.

The present invention is illustrated by the following example.

Example A thermal cracking was carried out in a furnace as shown in FIGURE 1. 657 m. /hr. (standard condition).

of petroleum cracking gas which was used as a fuel, 703 m. /hr. (standard condition) of oxygen and 1,261 kg./hr. of steam were burnt by means of burner. 1,487 l./hr. of naphtha as a raw hydrocarbon material for cracking were preheated to 500 C. and were injected into a combustion chamber from an injection nozzle were injected into a lower part of the combustion chamber from an injection nozzle at the velocity of Mach number 1 to mix it with the high temperature combustion gas and then the resultant mixed fluid was injected into a reaction chamber at the velocity in the throat passage of Mach number 1 to carry out a thermal cracking of naphtha. The reaction temperature was 1,120 C., the reaction time was 0.001 sec. and the amount of cracking gas was 2,122 mi /hr. (standard condition).

Furthermore, other tests were carried out with the same quantity of feed but at various flow velocities and by changing the flow velocity at the injection nozzle for raw material for cracking and also at the throat passage. The

The variation with lapse of time for the ratio of ethylene to acetylene to becaused. by the variations of the flow velocities at the injection nozzle and at the throat passage is'given in FIGURE 2. In FIGURE 2, the curve of the mark 0 represents the case of example, the curve of the mark X-represents the case of the comparative method 1, the curve of the mark I] represents the case of the comparative method 2 and the curve of the mark A represents the case of the comparative method 3.

As explained above,'the yield of acetylene and ethylene in the process of the present invention is highest and the formation on the wall of furnace of carbon and tar cannot be seen. From FIGURE 2, it is found that in the process of the present invention the ratio of ethylene to acetylene is not varied.

What we claim is: 1

1. A process for continuous thermal cracking of hydrocarbons in an elongated furnace comprising:

(a) producing a streamof flowing gases by first introducing combusting gases into a first zone of said furnace;

(b) secondly admitting hydrocarbon at a velocityat least equal to the speed of sound into admixture with the combusting gases at a point above a throat passage in said furnace;

(c) then flowing the admixed gases throughsaid throat passage at a velocity of at least the speed of sound;

(d) then introducing said gases into a second zone in said furnace wherein said hydrocarbon is thermally cracked;

(e) thereafter quenching the thermally cracking activity downstream of said second zone.

2. The process of claim 1 wherein the hydrocarbon is naphtha.

3. The process of claim 2 wherein the naphtha is preheated to about 500 C. before introduction into the first zone. 7

4. The process of claim 3 wherein the combusting gases are in a quantityto produce a temperature in the second zone of. 1,120 C. and the reaction time in said second zone is 0.001 seconds.

5. The process of claim 1 including admitting said hydrocarbon at the upper part of said throat passage.

6. The process of claim 1 including flowing said combustion gases at a velocity below the speed of'sound at a location above the throat passage and at the bottom of said first zone.

References Cited UNITED STATES PATENTS 2,767,233 10/1956 Mullen etal 260-679 2,790,838 4/1957 Schrader 260679 2,498,444 3/1950 Orr 260679 3,301,914 1-/1967 Donz et a]. 260679 FOREIGN PATENTS 996,202 6/1965 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

J. D. MYERS, Assistant Examiner.

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