US 3055957 A
Description (OCR text may contain errors)
Sept. 25, 1962 F. F. A. BRACONIER ET AL 3,055,957
PROCESS AND APPARATUS FOR PRODUCTION OF UNSATURATED HYDROCARBONS FilecLJune 3, 1958 3 Sheets-Sheet 1 Sept. 25, 1962 F. F. A. BRACONIER ET AL PROCESS AND APPAR OR PRODUCTION OF ATUS F ED HYDROCARBONS UNSATURAT 3 Sheets-Sheet 2 Filed June 5. 1958 u Z /iniiiii ATTORNE Sf Sept. 25, 1962 F. A. BRACONIER ET AL- 3,055,957 PROCESS AND APPARATUS FOR PRODUCTION OF UNSATURATED HYDROCARBONS Filed June 3, 1958 3 Sheets-Sheet 5 United States Belgium Filed June 3, 1958, Ser. No. 739,605 Claims priority, application Austria June 8, 19 57 7 Ciaims. (Cl. 26t)--679) This invention relates to a process for the thermal treatment of hydrocarbons and to furnaces for executing this process, and more particularly for preparation of unsaturated hydrocarbons, such as acetylene, ethylene and other olefines.
It is known that said unsaturated hydrocarbons can be produced by heating more saturated hydrocarbons for a very short time at high temperatures, either in the gaseous state or as liquids if finely dispersed, e.g., by spraying.
It is also known that to heat the hydrocarbons for pyrolysis, they may be introduced into the hot combustion gases of a flame. To promote high concentration of acetylene, or desired olefine, in the product gases, the dilution of the pyrolysis gases with inert gases is kept as low as possible. For this purpose, the burner is conveniently fed on one hand with oxygen containing only a small quantity of other gases, mostly nitrogen, and on the other hand with a fuel having a high caloric value, preferably a hydrogen-rich gas (e.g., more or less pure hydrogen, coke oven gas, etc.). The Water vapor formed by combustion of the hydrogen is readily condensed and separated from the pyrolysis gases.
In most of the previously proposed processes, the furnaces employed are of circular type, in which the fuel and the comburent gases (i.e., the combustion-supporting gases), after being separately led through concentric pipes, are mixed at the discharge point, outside the burner, with formation of a flame in the combustion chamber. The hydrocarbons to be pyrolyzed are then transversely or tangentially injected into the hot combustion gases of said flame; and, under the effect of the high temperatures there encountered, they are decomposed into unsaturated hydrocarbons. This decomposition takes place in the pyrolysis chamber, and is terminated at the end of said chamber by quenching, advantageously by a transverse water spray.
The present invention is an improvement on such processes, particularly from a thermal point of view.
In particular, the combustion reaction is carried out in a combustion chamber under conditions as adiabatic as possible with a minimum oxygen consumption.
To obtain this result, the following conditions are observed:
Preheatin'g the fuel and comburent gases at the highest feasible temperature;
Introducing said reagents into the combustion chamber under such flow rates and directions that mixing is substantially instantaneous and homogeneous, requiring consequently the least possible reaction time and allowing the use of a chamber having a small volume;
Reducing the losses of reaction heat through the walls of the combustion chamber.
When trying to meet these conditions, very high reaction speeds are easily obtained, with turbulence effects, which permit very small volume chambers. On the other hand, some very diflicult problems arise in the design of the combustion chamber, which has to resist very high temperatures while limiting as much as possible heat loss through the walls.
The radiation of the intense flame onto the walls and atent 1 3&55357 Patented Sept. 25, 1962 the turbulence inside the combustion chamber are so high that the refractory materials generally used for the construction of said walls would exfoliate rapidly. Metallic walls externally cooled With water do not offer a solution for the problem because of the high heat losses.
It is an object of this invention to overcome such shortcomings and to obtain conditions which substantially avoid caloric loss from the gases in the combustion chamber.
The process now to be used for making the unsaturated hydrocarbons from more saturated hydrocarbons according to this invention, comprises forming one or more rings of oxy-hydrogen flames projected in a direction parallel with the axis of the combustion chamber. By a further feature of invention, the walls are protected inside by a gaseous screen, particularly a screen of water vapor at a high temperature. Another gas having, like water vapor, an important absorption power for the radiation, may be used; but the separability of water by condensation, and its other properties, make water uniquely advantageous for this purpose.
The fuel gas and the oxygen are preheated to a high temperature adapted to reduce the oxygen requirements as much as possible and to obtain flames at very high temperature. Each of the preseated reagents is introduced into the combustion chamber through a series of perforations of small diameter arranged on a circle, each perforation for the introduction of the fuel gas is paired with (i.e., is counter-positioned to and in a common plane with) a perforation for the introduction of oxygen, whereby the resulting jets actually impinge.
These impinging jets of the reactive gases converge at an angle of at least The said perforations for these jets, moreover, have such dimensions that the gases have high outlet flow rates and substantially equal momenta.
With such disposal of the perforations for introducing the reaction gases, there results a circular series of elementary burners in each of which the mixing is realized in an efiicient and homogeneous way, very near but outside the gas distributor. The very short elementary flames of said burners merge into a substantially continuous and very short ring of flame, propagating in a direction parallel with the axis of the combustion chamber, but not contacting directly the inner wall of said chamber By thus concentrating the energy produced by said flames within a small chamber under substantially adiabatic conditions, the heat losses are reduced, but the inside Wall of said chamber would be subjected to a heavy radiation, were it not protected so as to avoid rapid deterioration. This protection is achieved with a ring of a vapor which acts as a radiation-protecting screen, and the inner wall is thus under good conditions of thermal resistance.
For the best efficiency of said screen, Water vapor is injected at high temperature as a continuous, homogeneous and full sheet, along the Walls of the combustion chamber.
In addition to its function as a thermal screen, water vapor may serve other advantages with respect to the yield and the economy of the pyrolysis process. Thus, it may transform a portion of the carbon monoxide of the combustion gases into carbon dioxide, which is more easily separated from the pyrolysis products. Without modifying the amount of the available calories, it makes it possible to cool the combustion gases, if their temperature is too high for the intended reaction, e.g., the production of ethylene or other olefines.
The nature and the advantages of this invention will be more apparent from the following description and the schematic representations in the example shown in FIG- URES 1 to 4.
FIGURE 1 is a section through an annular furnace for .for exit of the steam and an 12 and 12', with high the production of unsaturated hydrocarbons by injecting the hydrocarbons to be pyrolyzed into a flame ring.
FIGURE 2 shows, on a larger scale and in isometric view, a fragment of the furnace of FIGURE 1.
FIGURE 3 shows schematically a distributor adapted to be used in a large capacity furnace.
FIGURE 4 is a section through another type of furnace having a large capacity.
The annular furnace of FIGURE 1 comprises the distributor 1, the combustion chamber 2, and the pyrolysis chamber 3. Both chambers 2 and 3 have a continuous refractory wall 4. Pipes 5 and 6 provide for separately introducing the fuel gas and the oxygen through concentric annular conduits 7 and 8, each formed of spaced, concentric sleeves, passing through the distributor 1, for introducing these gaseous reagents in the combustion chamber 2. Pipe 9 feeds the hydrocarbon to be pyrolyzed through an annular header 9 and feed ports 22 in the chamber wall. Spray device 10 supplies water for quenching the pyrolysis gases and thus terminating the pyrolysis reaction.
On the inside of the combustion chamber, the distributor 1 is provided with an annular groove 11, coaxial with the pyrolysis furnace. The concentric rings 7 and 8 are fitted into corresponding slots in the distributor 1; and the sides of the groove 11, inclined to form an angle of not more than 90, are perforated with holes 12 and 12 which connect said slots and the annular conduits 7 and 8 with the combustion chamber 2.
FIGURE 2 shows, on a larger scale, a part of this annular groove 11.
The diameter of said holes 12 and 12 is such that:
(1) Each of the fluids has a high outlet flow rate, advantageously in the range 100-200 m./sec.; and
(2) The momenta of both fluids coming out from the adjacent counter-positioned holes 12, 12' are substantially identical.
A cooling system may be provided to protect the distributor 1 from adverse eflects of the intense radiation of the flame in the combustion chamber. This is illustrated in the drawings by the pipes 13 and 14 through which cold water is circulated to and from the annular passages .15 and 16, and the pipes 17 and 18, through which cooling water circulates to and from the central water jacket 17 in the distributor 1.
An annular steam distributor ring 19 is provided on the wall 4 below the distributor 1. A narrow slit 20 provides annular guide 21 directs the superheated steam along the refractory wall 4 of the combustion chamber 2, thus thermally protecting said wall.
Perforations 22 for injecting said hydrocarbon from feed pipe 9 are positioned at the top of the pyrolysis chamber, below the combustion chamber.
Preheated hydrogen, or hydrogen-rich gas, and oxygen are fed through pipes 5 and 6 and concentric conduits 7 and 8, into combustion chamber 2 through the perforations outlet flow rates and substantially equal momenta.
These gas flows impinge on one another, coming together at an angle of at least 90. This provides eificient and homogeneous mixing with the formation of a ring of short flames extending in the direction of the axis of the combustion chamber, thus making it possible to use a chamber with a small volume.
The energy produced by said flames is concentrated and the heat losses are reduced, but it is advisable to thermally protect the wall 4 of the combustion chamber 2 with a screen of water vapor, which is injected as a ring through slit 20 and along guide 21.
At its bottom, the combustion chamber is open to the pyrolysis chamber. Here, the super-heated steam of the protecting screen, passing into and through the pyrolysis chamber, is mixed with the hydrocarbon injected through the perforations 22 transversely to the direction of said steam flow.
The hydrocarbon is pyrolyzed in chamber 3 into acetylene and/ or ethylene or other olefines under the effect of the high temperature. The resulting pyrolysis gases are quenched at the bottom of chamber 3 by transversely injecting cold water through a sprayer 10.
This type of furnace is particularly suitable for average capacities for the production of pyrolysis gas; but even for greater capacities, the principle of the flame rings and the water vapor protection screen with a relatively small combustion chamber may be also applied.
According to a particularly advantageous embodiment of this invention, the burner may comprise several pipes feeding oxygen and hydrogen so that several concentric flame rings are formed in the combustion chamber. By way of example, FIGURE 3 shows such a burner and furnace, for which that principle has been used.
The reference numbers have the same signification in FIGURE 3 as in FIGURE 1. The fuel gas and the oxygen are fed through pipes 7 and 8, and come into the three annular grooves 11 through a series of opposite perforations 12 and 12', thus forming at the outlet of distributor 1, in the combustion chamber 2, three rings of flame. The wall 4 of the combustion chamber is protected from the radiation of the flames by a screen of water vapor originating from the collector 19 and passing through the slot 20 and along the guide ring 21.
According to a modified embodiment, water vapor may be additionally fed into the combustion chamber through a series of perforations distributed between the annular notches 11, so as to form additional rings of water vapor between the flame rings. Consequently, the thermal conditions and the reaction state are more homogeneous in each cross section of the combustion chamber, in which the combustion gases are located.
Another embodiment of this invention, which is particularly advantageous for the realization of industrial units with a large production, comprises using an annular furnace, such as is schematically represented, by way of example, in FIGURE 4.
The combustion chamber 2 is annular and situated between the side wall 4 and the annular ring 23', it is provided with a wall 24 of refractory ceramic or metallic material, and it is cooled with cold water circulating in jacket 25.
The fuel gas and the oxygen fed through the pipes 7 and 8, respectively, are intimately mixed in the annular groove 11, at the outlet of distributor 1, forming a ring of oxyhydrogen flames in the annular combustion chamher 2. The Walls 4 and 24 of said combustion chamber are protected from the radiation of the flame ring by screens of water vapor originating from the collectors 19 and 26, respectively, injected through slits 20 and 27 and guided by the annular plates 21 and 28.
The hydrocarbon to be pyrolyzed is injected into the superheated steam leaving the combustion chamber 2, through a series of perforations 22 and 22, distributed on two concentric and annular rings situated on the periphery of the combustion chamber 2 and on the central ring 23, respectively. The hydrocarbons are fed to these perforations in two separate streams through pipes 9 and 9'. By thus directing jets of the hydrocarbon to be pyrolyzed against one another and transversely to the direction of the flow of the overheated water vapor, a complete mixing of the reactant gases is obtained.
The pyrolysis gases are quenched by transversely injecting water through the sprayers 10 and 10'.
This type of annular furnace, with one or several flame rings is particularly advantageous, since it makes it possible to treat important quantities of the hydrocarbons to be pyrolyzed under homogeneous operating conditions, as well in the combustion chamber as in the pyrolysis chamber, even in furnaces of large dimensions. In fact, if one uses central rings 24 of diameter depending on that of the furnace (i.e., greater when the diameter of the furnace is greater), the conditions for penetrating and diffusing the gaseous hydrocarbons into the combustion gases can be kept the same.
It is to be understood that the abovedescribed examples are given for the purpose of illustrating the invention and its principles and showing others skilled in the art how it may be used to advantage and it may be also modified. Thus, water may be injected along the walls of the combustion chambers, said water being evaporated under the effect of the high temperatures of said chambers, and forming a thermal screen. This operating method is particularly interesting when it is desired to cool the combustion gas for the pyrolysis of hydrocarbons into olefines.
The following examples are illustrative:
Example 1 The furnace represented in FIGURE 1 is used for the simultaneous production of 2 tons/day of acetylene and 2.5 tons/day of ethylene. The combustion chamber 2, delimited by the distributor 1 and the wall 4, both of refractory material, has an internal diameter of 140 mm. and a height of 160 mm. Distributor 1 comprises an annular notch 11, the sides of which are each inclined on 45, while being provided with 24 perforations 12' with a diameter of 7 mm., said perforations being distributed on a ring with a diameter of 104 mm., and with 24 perforations 12 of 4.5 mm., distributed on a ring with a diameter of 66 mm.
Coke oven gas, preheated to a temperature of 450 C. and having the following composition:
Percent by volume is fed with a throughput of 5,200 Nm. /day (cubic meters per day, calculated to normal conditions, i.e., 0 C. temperature and 760 mm. pressure), through pipe 6 and annular passage 8, and is introduced in the combustion chamber through perforations 12'. 96% pure oxygen, also preheated to 450 C., enters the combustion chamber 2 by passing through pipe 5, annular passage 7 and perforations 12, its throughput being at the rate of 4800 Nmfi/day.
When entering the combustion chamber, said gaseous reagents interpenetrate, meeting at an angle of 90, and igniting to form a flame ring. The latter, propagating in a direction parallel with the axis of the combustion chamber, is surrounded within the wall 4 of said chamber, by a screen of water vapor at 700 C., coming from the distributor 19 with a throughput of 8 metric tons/ day and under a gauge pressure of 2 kg./cm. The slit 20* is 1 mm. in width.
The perforations 22 are 160 mm. below the distributor 1. 4070 Nm. /day of a propane-butane mixture, preheated at 350 C. and having the following composition:
Percent by volume Propane 82.3 Butane 15 .3 Butene 2.4
For treating larger quantities of gas, an annular furnace as represented in FIGURE 4 is advantageously used.
The annular chamber 2 surrounds a central ring 23 75 having a diameter of 200 mm. The chamber 2 is limited by a refractory wall 4 at a distance of 70 mm. from the refractory wall 24. It is 1 60 mm. in height between the distributor 1 and the devices 22 and 22' for injecting the hydrocarbons to be pyrolyzed.
The coke oven gas, fed through pipe 8, is introduced in the combustion chamber through 100 perforations 12 having a diameter of 7 mm. and distributed on a circle having a diameter of 294 mm. Oxygen is fed through pipe 7 and introduced through 100 perforations 12, each having a diameter of 4.5 mm., and distributed along a circle of 246 mm. diameter.
The refractory walls 4 and 24 of the combustion chamber are thermally protected with water vapor injected under pressure of 2 kg/cm. through the slits 20 and 27, each of 1 mm. width.
By using 16,800 Nmfi/day of coke oven gas heated to 450 C. (having the same composition as that given in the preceding example), 22,800 Nm. /day of oxygen at 700 C. (actual volume is greater by the amount of impurities as this is calculated on the basis of 100% oxygen) and 3.2 metric tons/day of vapor at 700 C., a pyrolysis gas containing 8 metric tons/day of acetylene and 9.25 tons/day of ethylene (calculated on dry gas) is obtained by injecting 19,000 Nmfi/day of a mixture preheated at 350 C. and comprising 82.3% by volume of propane and 15.3% by volume of butane (the remainder being butene).
What We claim is:
1. A furnace for production of acetylene, ethylene, or other olefines by pyrolysis of more saturated hydrocarbons which comprises annular conduits for feeding, respectively, fuel and comburent gases, a distributor for said gases, a combustion chamber and a pyrolysis chamber, said combustion chamber having a small volume, said distributor being provided, on the face thereof adjacent to said combustion chamber, with an annular groove coaxial with said combustion chamber and with the annular conduits for feeding the gaseous reagents, the sides of said groove diverging at an angle not greater than and having small perforations connecting said groove with said annular conduits, said perforations communicating with the conduit for introducing one of the gases being paired with corresponding perforations for introducing said other reactive gas, a steam distributor ring adjoining the combustion chamber and spaced from the inner periphery thereof adjacent to the distributor for reactive gases, said steam distributor being provided with a narrow slit for injecting steam longitudinally adjacent the wall of the combustion chamber.
2. A furnace according to claim 1, wherein the combustion chamber is annular, being provided throughout its length with a central core.
3. A furnace according to claim 2, wherein the wall of the central core is provided with passages for circulating coolant, and a steam distributor ring is provided therein adjacent the distributor for the reactive gases whereby the core is externally protected by a screen of water vapor.
4. A furnace according to claim 1, wherein the distributor for the reactive gases is provided, on its side toward the combustion chamber, with several of said concentric annular grooves and between them are provided steam distributor rings for flowing a curtain of steam around the rings of flame formed by the perforations in said grooves.
5. In a process for pyrolysis of saturated hydrocarbons for the production of unsaturated hydrocarbons by rapid heating in a combustion chamber by the hot combustion gases of a fuel gas flame therein, the steps which comprise separately introducing into said combustion chamber at one end thereof said fuel gas and a comburent gas for forming said flame, each of said gases being introduced in a plurality of pairs of separate streams at flow rates of about -200 ma/sec. and with substantially equal momenta and each said pair including a stream of said fuel gas and a separate stream of said comburent gas impinging on each other at an angle of at least 90 C. and at a point axially spaced from said end of said combustion chamber, said plurality of pairs of separate streams being distributed within said combustion chamber so that said points of impingement of said separate streams form a generally circular configuration across said combustion chamber and inwardly spaced from the periphery thereof, igniting said fuel and comburent gases at said points of impingement of said separate streams thereof forming a ring of a plurality of short flames which extend axially of said chamber and inwardly spaced from both said end of said chamber and said periphery thereof for concentrating the heat energy produced by all said flames axially of said chamber and away from the periphery thereof, injecting said hydrocarbon to be pyrolyzed radially into said combustion chamber and into said hot combustion gases from said ring of flames therein at a point spaced axially of said combustion chamber from said ring of flames therein for pyrolyzing said hydrocarbon with the heat from said ring of flames, and quenching the products of the pyrolysis reaction for arresting said pyrolysis at a point in said combustion chamber where pyrolysis of said injected hydrocarbon by heat from said ring of flames has achieved pyrolysis production of said unsaturated'hydrocarbon.
6. A process as recite also introduced into sai said ring of flames adjacent sai screen of heat-insulating vapor products of said flames, and vapor flowing a for enclosing combustion References Cited in the file of this patent UNITED STATES PATENTS Metzger Nov. 7, 1939 Hartwig et al Oct. 23, 1951 Jones Mar. 16, 1954 Mullen et al Oct. 16, 1956 Cunningham Sept. 3, 1957 Braconier et a1. Feb. 4, 1958 Fox Jan. 13, 1959 Hale et al Jan. 13, 1959 Kircher et a1. Mar. 15, 1960 Schultz Mar. 22, 1960 Krause et al June 14, 1960 FOREIGN PATENTS Belgium Dec. 9, 1953 d in claim 5 in which there is d combustion chamber around d end of said chamber a maintaining said screen of Xially of said chamber and between said