US 3047371 A
Description (OCR text may contain errors)
July 31, 1962 w. KRAUSE ET AL DEVICE FOR CARRYING OUT CHEMICAL REACTIONS AT HIGH TEMPERATURES Filed Aug. l5, 1958 i 2 7.111111111111111? t 1 :tt-:12| 3 coMeusr/afv HAI/WSE@ 6004/4/6 46E/VT W E@ K E VM ACR@ 0 ew/s n wr eea E im M 45u WW@ 3,047,371 DEVHCE FOR CRRYENG GUT CHEMICAL REACTIONS AT HEGH TEMPERATURES Walter Krause, Frankfurt am Main, Werner Fischer, Bad
Soden (Taunus), and Rudolf Wirtz and Hartmut Schiltken, Frankfurt am Main, all in Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius @c Brning, Frankfurt am Main, Germany, a
corporation of Germany Filed Ang. 13, 1958, Ser. No. 754,900 Claims priority, application Germany May f3, i955 1 Claim. (Cl. 23-277) The present invention relates to a process and to a device for carrying out chemic-al reactions at high temperatures.
This application is a continuation-impart of application Serial No. 583,567 led May 8, 1956, now U.S. Patent 2,941,021 granted June 14, 1960.
It is known that the production of acetylene, ethylene and higher oleilns from starting materials, such as methane, ethane or higher hydrocarbons, requires supplying an application of great amounts of energy to the starting materials within the shortest possible time.
Thus, for example, the energy may be supplied indirectly by passing the gases to be cracked through externally heated pipes or heat exchangers. This method involves the disadvantage that, in order to effect a transfer of the required amount of heat, the walls of the pipes must be heated to a higher temperature than that desired for the reaction, and thus give rise to pronounced formation of coke and soot. Furthermore, the process referred to above is restricted to the use of small diameter pipes, since a pipe of larger diameter is inherently incapable of effecting a rapid and complete heat transfer from the walls to the gas. The gases in the boundary zones become too hot whereas the gases in the interior zones are heated sufficiently and, therefore, do not participate in the reaction.
The so-called regenerative furnace has also been proposed for providing a means of indirect heat exchange. Such a furnace, and the heat-absorbing filling material it contains, is initially heated with a gas mixture obtained by combustion of fuel with air; heating is then interrupted, the furnace is cleansed with an inert gas and then charged with the hydrocarbons to be cracked at the hot filling material of the furnaces. The furnace is again heated with heating gas after a minimum cracking temperature has been reached. This cycle of operation is continually repeated by automatic means at intervals of some minutes. This process has, in addition to the complicated automatic reversing means, the disadvantages of involving an inevitable deposition of tarry substances in the regenerative furnaces and the constantly changing temperature of the furnace, all of which jeopardize economy and the yields obtained.
According to the so-called partial oxidation process the energy required for cracking is supplied directly by subjecting part of the hydrocarbon to be cracked to a combustion process with oxygen in a special combustion device, whereby the hydrocarbon itself furnishes the energy for pyrolizing the excess hydrocarbon. This process is however not applicable when it is desired to avoid partial combustion of the hydrocarbon to be cracked.
Therefore, it has repeatedly been proposed to supply the energy by means of carrier gas, for example hydrogen or combustion gases such as steam heated to a high temperature, which is then mixed in suitable manner with the hydrocarbons to be cracked. In this case, it is especially advantageous to use hydrogen as fuel and to subject this subst-ance together with oxygen to a combustion process since, after the reaction, the steam formed can be easily separated from the resulting gas by condensation and since the subsequent separation of the gas is thereby rendered less difficult. However, other products obtained by combustion of any combustible substance may be used as combustion gas.` Furthermore, it is particularly advantageous to burn the fuel within a fairly small space and to provide for as short a distance as possible between the end of the combustion zone and the point, Where the hydrocarbon to be cracked is admixed to the combustion gas, so that the inevitable heat losses caused by dissipation are kept as small as possible.` As results therefrom, it is desirable to produce a fairly short flame which furnishes great amounts of energy but burns only for a short distance. To this end, the fuel and the oxidizing agent are often pre-mixed in a separate lmixing chamber before they are introduced into the combustion chamber for combustion. The combustion devices which are supplied with pre-mixed gases involve however the risk of flash back into the mixing chamber and consequent destruction of the combustion device unless the gas supply lines are provided with very sensitive and in most cases technically complicated control devices which maintain constant pressure and velocity of flow of the mixture of oxygen and vaporized or gaseous fuel, such as hydrogen, as is the case with combustion devices used for the incomplete combustion of methane or earth gas with oxygen.
All these disadvantages are overcome by ourpresent invention. The apparatus of the invention comprises' a lbustion chamber for performing pyrolytic reactions, especially the production of acetylene and/or ethylene and/or higher olefinic hydrocarbons, wherein fuel and oxidizing agent are completely mixed only after the components have reached the flame so that just as short a flame is produced as in the case where the flame is produced by the supply of preunixed gases. According to the process of this invention, finely divided liquid, vaporized or gaseous fuel and at least one oxidizing gas are introduced separately into the combustion chamber at a velocity corresponding to a Mach-number of at least 0.8, preferably at sonic speed, which is attained as soon as the ratio of the absolute pressure at which the gases are introduced into the combustion chamber by the bore holes to the absolute pressure 'in the combustion chamber is about 2:1, through at least one bore hole each for the fuel and the oxidant, and then subjected to a combustion process. The bore holes are arranged tangentially in one or more planes. One of the reactants may be introduced Wholly or partially via'radial bore holes. By mixing-and whirling in the manner described above, fuel and oxidizing agent undergo so rapid a combustion that the resulting flame ceases to burn after a very short distance. 'It is, therefore, possible to operate the combustion chamber with very high charges.
Industrially, it is especially advantageous'y to operate the combustion'chamber with charges of one billion or more Kcal./m.3h. (109 Kcal.). The combustion chamber as used in the process of this invention. has the particular advantage that the 4whole combustion process is performed within a small space-as is the case of llames produced with pre-mixed gases-so the heat losses caused by dissipation are small in relationA to the energy produced; contrary to the known devices, a combustion charnber -as used herein prevents the llame from flashing back into the mixing chamber and requires no complicated control mechanism.'
The term Mach-number is used herein to define the gas velocity applied in relation to the sonic speed at the corresponding temperature. The operating procedure according to this invention involves the further advantage that the combustion gases leaving the combustion chamber at flame temperature Patented July 31, 19152-v possess such a high turbulence-due to their having been whirled in said chamber-that they are practically instantaneously mixed with the reactant to be pyrolized. Thus, the heat is rapidly and effectively transferred from the combustion gas to the reactants, whereby it is possible to perform a practically complete reaction.
It is within the scope of the invention to introduce the reactant to be pyrolized in any desired direction into the exit of the combustion chamber e.g. radially or tangentially either in or opposite to the direction of rotation or in any desired angle to the wall of the combustion chamber. Furthermore, it may be advantageous to force the combustion gases, prior to being mixed with the reactant, through a contracted opening, for example a nozzle, in order to increase their axial velocity.
In carrying out the process of this invention it has proved particularly advantageous to arrange the bore holes for the introduction of the fuel and the oxidizing agent, respectively, in a manner such that each opening for the supply of fuel is adjacent openings for the supply of the oxidizing agent and vice versa. rIhe fuel and the oxidizing agent may, however, also be introduced through bore rings, which may be arranged in more than one plane substantially parallel to each other and distant from each other in the direction of the longitudinal axis. It is particularly advantageous to arrange -substantially all bore holes for one or all reactants tangentially to the longi- Ytudinal axis of the combustion zone.
When it is desired to prepare acetylene and/or ethylene and/ or higher olefin-containing gases, i.e. gases which in addition to acetylene and/or ethylene contain propylene, n-butylene, iso-butylene, etc., that is chiefly olefins with 3 or 4 carbon atoms, it is especially suitable to admix between the flame end and the place where the reactant is introduced a secondary gas, preferably steam and/or hydrogen in order to reduce the proportion of oxygen-containing radicals, oxygen atoms and oxygen molecules as it is described in copending patent application Serial No. 578,581 filed April 17, 1956 for: Manufacture of Low Molecular Unsaturated Hydrocarbons. This operating procedure is especially suitable if fuels are used that produce flames and combustion gases, such as have very high temperatures, for example hydrogen. In this case, the secondary gas can be introduced into the combustion gas tangentially either in or opposite to the direction of rotation, radially or in any desired angle to the wall of the combustion chamber.
For the productionrof acetylene and/or ethylene and/ or other olefins containing two to four carbon atoms using a combustion device according to this invention, aliphatic hydrocarbons which may have been pre-heated are introduced in liquid or gaseous form-which term here and below shall include the vaporized state-either radially or tangentially or in any other known manner into the current of combustion gases in order to be mixed with the latter gases rather rapidly and completely, and the reacted mixture is chilled in known manner after a short time of reaction, for example by injection of water. In this case it is especially advantageous to line the reaction chamber, for example the reaction tube, with ceramic materialY tov suppress undesirable soot formation which is favored by metal surfaces.
For designing the combustion chamber it is expedient to` use a metal which is cooled by means of a cooling agent, for example water; however, there may also be used ceramic material or metal lined with ceramic material. In the case of a cooled metal combustion chamber, the heat taken up by the cooling agent can be recovered and used for other purposes.
As starting materials suitable for use in the process of this invention there can be used the known hydrocarbons, for example saturated or unsaturated hydrocarbons containing up to 30 or more carbon atoms. It is particularly advantageous to employ saturated hydrocarbons, such as methane, ethane, propane, butane, pentane, heptane, oc-
tane, decane, dodecane, especially in the form of liquid commercial mixtures, `such as petroleum distillates or hydrocarbon oils, for example topped Arabian or Kuweit oil, as well as in the form of technical gases such as earth gas. Branched chain hydrocarbons, for example isobutane, isooctane, isoheptane, etc., may also be used in addition to or instead of aliphatic saturated hydrocarbons containing from l to about 30 or more carbon atoms. It is not advisable to use unsaturated hydrocarbons per se unless it is desired to produce acetylene or unless they are contained in small amounts in other hydrocarbons. Thus, for example, ethylene, propylene, nor iso-butylene may be used for the production of acetylene.
As fuels suitable in the production of acetylene and/ or ethylene and/ or higher hydrocarbons there may be used any gaseous or other hydrocarbons that are liquid or solid and can be liquefied by heating. Such fuels are used in a finely divided form for operating the combustion chamber according to this invention and for the production of the aforesaid unsaturated hydrocarbons. The term finely divided form as used herein is intended to include finely atomized liquid as well as gaseous and vaporous forms of hydrocarbons. Hydrogen, carbon monoxide or water gas which contains an excess of hydrogen and/ or carbon monoxide, or gas mixtures which are obtained in the present process after separation of the acetylene and the desired olens are also useful as Such gas mixtures may e.g. contain hydrocarbons in addition to hydrogen and if desired carbon monoxide. In some cases it is advisable to use commercial hydrogen.
As oxidizing agent there may advantageously be used commercial, pure oxygen, or an oxygen-containing mixture such as air, the oxidizing agent being always ernployed in a theoretically insufficient quantity.
One preferred embodiment of the apparatus of the invention that is suitable for use in carrying out the process of this invention is shown diagrammatically in the accompanying drawing, wherein:
FIGURE 1 is a schematic view in elevation; and
FIGURES 2 and 3 are sections taken through section lines A-A and B-B, respectively, of FIGURE 1.
In the drawing the numerals designate the following parts: Metal chamber 1 surrounded by a cooling agent, for example water, is supplied through tangential bore hole 2 with hydrogen and through tangential bore hole 3 with oxygen. As shown in FIGURE 2, hydrogen and oxygen are supplied alternately in one or several superposed planes. Secondary gas is introduced radially or tangentially or in any desired angle to the wall of the combustion chamber by way of inlets 4 at the end of the ame. The hydrocarbons to be cracked are also introduced radially or tangentially or in any desired angle to the wall of the combustion chamber by way of inlets 5 as shown in FIGURE 3. After a short residence time in reactor 6, depending on the dimensions of the reactor and the velocity of the gases, the gases are chilled by means of a cooling agent, for example finely sprayed water introduced by way of lines 7, and separated in a siphon 8 from the liquid ingredients. The reactor is constructed of metal resistant to high temperature and provided with a cooling jacket 9.
Example 28.3 Nm.3 of hydrogen, kept under a pressure ofA 4.3 at. (absolute) and 13.6 Nm3 of oxygen, kept under a pressure of 5.5 at. (absolute) are introduced tangentially at room temperature into a combustion chamber in which the pressure is about 1.5 at. (absolute) both gases are accordingly introduced with sonic velocity into said combustion chamber, where they react completely with each other. To the combustion gases thus obtained Z1 kilograms of steam having a temperature of C. are admixed per hour through tangential bore holes and then 13.6 kilograms per hour of a vaporous light gaso- 50.4 hydrogen 1.5 N2 and Ar (from oxygen) 8.2 carbon monoxide 0.8 carbon dioxide 13.1 methane 10.0 ethylene 15.3 acetylene 0.1 propylene 0.6 ethane We claim:
In an apparatus for carrying out a pyrolysis of hydrocarbons with contacting hydrocarbons `with a stream of hot combustion gases, a combustion chamber for producing a continuous stream of said hot combustion gases, said combustion chamber having a closed end, a metal side wall for contact with said hot combustion gases, a cooling jacket for said side Wall, and bore holes for separately introducing fuel and an oxidizing gas therefor, said bore holes being .adjacent said closed end and tangential to said side Wall, and said apparatus having a contracted opening between the combustion chamber and the place Where the hydrocarbon to be pyrolized is introduced.
Ekholm June 10, 1952 Mullen et al. Oct. 16, 1956