US3057707A - Process for treatment of hydrocarbons - Google Patents

Description

Oct. 9, 1962 F. F. A. BRACONIER ET AL 3,957,707

PROCESS F OR TREATMENT OF HYDROCARBONS Filed Feb. 2. 1959 2 SheetsSheet 2 United States Patent Office 3,057,707 Fatented Oct. 9, 1962 PROCESS; FOR TREATMENT OF HYDROCARBUNS Frdric Francois Albert fsraeonier, Plainevaux, and dean Joseph Lambert Eugene Riga, Liege, Belgium, assignors to Socit Beige de lAzote et desProduits Chimiques du Marly, Liege, Belgium Fiied Feb. 2, 195 Ser. No. 790,568 9 Claims. (Cl. 48-496) This invention relates to a process and an apparatus for rapidly extinguishing the furnaces for the partial combustion of hydrocarbons, used for the preparation of less saturated hydrocarbons such as acetylene and olefines, or synthesis gas consisting mainly of carbon monoxide and hydrogen.

It is known that said furnaces for the partial combustion comprise, as essential parts, a chamber for mixing the reagents (gaseous or vaporized hydrocarbon and oxygen), a partial combustion chamber communicating with the preceding chamber, e.g., through a distributor or a grating for distributing the gaseous mixture, and a device for quenching the resulting mixture to terminate the pyrolysis reactions.

It is also known to reduce the oxygen consumption by preheating the reagents at a high temperature, which is however lower than that which would produce a spontaneous ignition of the hydrocarbon in the mixing chamber. For preventing the flame formed in the combustion chamber from propagating in the mixing chamber, the linear velocity of the gaseous reagents is kept higher than that of the flame propagation.

Even with proper design, however, there remains some danger due to accidental causes, such as the variations of the throughput and the composition of the gaseous reagents, that backfiring may occur. In such event the hydrocarbon to be pyrolyzed takes fire in the mixing chamber. It is thus desirable to make provision for extinguishing such flame as soon as possible to avoid important loss or even a complete destruction of the distributor and the mixing chamber.

Numerous expedients have already been proposed or experimented with for this purpose. However, they have failed due to the lack of sensitivity of the combustion detector in the mixing chamber and because of the arrangement taken for extinguishing the furnace. Most generally blowing nitrogen into said chamber and substituting nitrogen streams for the streams of the gaseous reagents are not sufficiently rapid and efiicient.

The present invention overcomes these drawbacks and makes it possible to extinguish the furnace even in a fraction of a second, when a pre-ignition occurs in the mixing chamber.

One process according to this invention utilizes an instantaneous temperature detecting means to respond to pre-ignition in the mixing chamber. Such means may with advantage he a bare thermo-couple located in the bottom of said chamber, near the distributor. Said thermo-couple when heated by the pre-ignition gives an electric signal which is used to trigger the starting up, auto matically and simultaneously, of the following operations.

(1) Closing the conduits feeding the gaseous reagents by means of valves situated on the cold portion of said conduits, i.e. upstream beyond the preheaters for said reagents.

(2) Flooding with nitrogen the conduit which has been feeding the hydrocarbon to be pyrolysed.

(3) Blocking the oxygen in the preheating section by blowing nitrogen into the oxygen conduit at a point as close as possible to the mixing chamber.

(4) Closing the product gas outlet conduit.

(5) Opening a venting device for venting gases from the pyrolysis furnace.

(6) After a suflicient period for complete purging of the hydrocarbon feeding section, nitrogen is then introduced in the oxygen feeding conduit, just downstream the closing valve of said conduit.

These six different operations for opening and closing the conduits are realized by means of automatic valves driven simultaneously for the first five of these operations and With a slight delay for the last operation. The thermocouple in the case of a pre-ignition in the mixing chamber, transmits an impulse to a signal-responsive valve operating device e.g., consisting of several electromagnetic relays with contacts, each valve being driven by an individual electromagnetic device controlled by one of said relays, as hereinafter more specifically described.

To secure the maximum safety of the process, closed circuits through the relay contacts are used, i.e. during the normal run of the furnace, all the contacts are closed and only when a pre-ignition occurs in the mixing chamher, the impulse transmitted by the detecting thermocouple causes the opening of the contacts and the automatic working of the valves controlled by the relays.

When using the inverse method, i.e., when the driving relays of the valves are operating by closing the contacts (the latter being open at a normal run of the furnace), it is still to be feared that, due to the oxidation of the contacts, the closing of the latter may be hindered.

The invention herein disclosed is designed to avoid damage, in such cases, by very rapid and fully efficient operation of said valves. To this end certain conditions are controlled as will be disclosed hereinafter, as applied to a partial combustion furnace schematically represented in the accompanying drawing showing such apparatus partly in vertical section, partly in diagrammatic layout.

Said furnace, in the example shown, is of the type covered by our copending application Serial No. 726,248, filed April 3, 1958. As here shown, the furnace comprises an annular feed-commingling zone 1, for contacting and intimately mixing the gaseous reagents, said zone being extended to an annular final mixing chamber 2 widening downwards and surrounding a central hollow conical core 3, the apex of which is at the center of the distributor 4. The distributor 4 connects said mixing chamber 2 to the pyrolysis chamber 5 including the device 6 for quenching the product gases by transversely injecting cold water.

The conduit 7 connected to the oxygen supply is provided with an automatic shut-off valve 8 and with a preheater 9. Conduit 7 projects into the hollow central core 3, as shown. The conduit 10 for introducing the hydrocarbon to bepyrolyzed in the mixing device is also pro- The conduit 13 for carrying off the cooled pyrolysisgas es to the acetylene purification and concentration unit, is provided with an automatic shut-off valve 14 and a device 15 for venting the gases when said valve is closed.

The temperature-responsive device for detecting a spontaneous ignition, or back-firing, in the mixing chamber,

is shown diagrammatically as a bare thermo-couple 16, projecting several centimeters into the mixing chamber 2, near the distributor 4. The conduits 17, 18 and 19, provided with automatic valves 20, 21 and 22 respec.

tively, are used to blow in nitrogen under pressure for rapidly extinguishing the furnace when any combustion.

occurs in the mixing chamber 2.

The bare thermo-couple is connected to a relay box 3 comprising eight open electromagnetic relays, the magnetic winding circuits of which are energized (after amplification) by the thermo-couple 16, and their contact circuits driving the solenoid valves 8, 11, 14, 20, 21 and 22 and the valves (not shown) for closing the circuits of the fuel fed to the preheaters 9 and 12.

At a normal run of the furnace for the partial combustion, the electromagnetic contacts and the automatic valves 20, 21 and 22 are closed and the valves 8, 11 and 14 are open. Oxygen fed through conduit 7 and heated to a temperature of about 600 C. in the preheater 9, is introduced in the mixing zone 1, where it is mixed with the hydrocarbon to be pyrolyzed, fed through conduit and also preheated to about 600 C. in the preheater 9. The gaseous reagents are completely mixed in chamber 2 and then, passing through the parallel pipes of the distributor 4, they enter the pyrolysis chamber 5, where they are ignited. The gaseous reaction products are cooled by transversely injecting water from the sprayer 6, whereafter they pass off through conduit 13 to the acetylene purification and concentration unit.

One example of valves and valve control circuits is shown diagrammatically in FIGURE 2. On each of the inlet lines and on the outlet line is an emergency shutoff valve: 8 for the oxygen feed line 7, 11 for the hydrocarbon feed line 10, 14 for the product gas exit line 13, and 26 for the preheater fuel line 25. For quick operation these valves are illustrated as sliding gate valves of the guillotine type having operating levers, sufficiently weighted at 30 to close the valve immediately when released, and a magnetic latch mechanism 31 adapted so long as it is energized to hold up the valve and the weight 30 during normal operation but instantly to release them when the electromagnetic coil 32 is deenergized.

A supplementary shut-otf device is shown in this example, i.e., the pneumatically operated flow regulator valves 35 and 36, respectively, for the oxygen and methane supply lines. These are shown as spring-operated to closed position and pneumatically operated to open position, being regulated for normal operation by pneumatic pressure lines with pressure-control devices represented by the squares 37, 38; but, for purposes of this invention, solenoid-operated valves 39, 40 are connected between the control devices, 37, 38 and the regulator valves 35, 36. Normally, these solenoid valves merely connect the pneumatically operated valves 35, 36 through the regulators 37, 38, to the pneumatic pressure lines; but, when the solenoid is operated by an emergency signal from the temperature-sensing device 16, these valves 39, 40 close the connections to the regulators, 37, 38 and vent the pressure line from the valves 35, 36, so that each valve is closed by action of its contained spring.

Similar valves 20, 21 and 22 control the emergency supply of a smothering gas such as nitrogen. Valves 5 and 22 are normally pneumatically held closed against the pressure of their springs 41, and are opened by the pressure of the springs when the pneumatic pressure on the pneumatic diaphragms 41 is vented by operation of valves 44 when the magnetic coils 45 are energized. 6

Valve 21 is inverted, in that it is normally held closed by the spring and is opened by pneumatic pressure.

The electrical circuit for emergency closing of the valves connects all the solenoids 32 and 45 for valves 14, 20, 22, 35, 36, 8, 11 and 26 and the relay 56 in parallel with each other from the power source 47 and in series with relay 48 which completes the circuit for all the valves back to the power source 47. Similarly, supervisory alarms will ordinarily be used on the compressed air and smothering gas lines, to be sure that they are always ready for emergency operation.

The electrical circuit, as shown, being an emergency protective device, should ordinarily be designed for closed circuit operation with the usual supervisory alarms (not shown) to warn of any failure in the circuit.

With the circuit thus closed in normal operation, the armatures of the solenoids 32 are pulled up (as shown), the connected bell cranks being swung about their fixed pivots 50 so as to push home the latch bolts 31 to engage under the catches on the valve stems, as shown. The valve stems are urged down against the latches by the weighted levers 30 pivotally mounted at 51.

The solenoid-operated valves 39 and 40 are held in their upper position, as shown, where the upper vent passage is closed and the lower passage connects the air pressure to the diaphragm chamber 42, so that the air pressure pushes down the diaphragm and the valve stem connected to it.

The same is true of valves 20 and 22, but with the valves 20 and 22 pushing down the valve stem closes the valve, whereas the valves 21, 35 and 36 are opened when their stems are similarly pushed down. The valve 21 is similarly operated, but is energized through a delay relay 55, the delaying device of which is set to delay closing of the circuit sufiiciently after the temperature limit is reached at 16, so that purging of the mixing chamber and furnace begins before additional oxygen in the pipe 7 is pushed along by the nitrogen admitted at 18.

The opening of relay 48, by action of the temperatureresponsive device 16 de-energizes all of the coils 32, and E6. Valves 8, 11, 26, 35, 36 and 14 are therefore immediately closed, to isolate the mixing chamber and furnace from the reagent supplies and the product treating systems; valves 22 and 20 are immediately opened to flood the isolated part of the apparatus with the smothering gas; and only later, after the predetermined delay, the valve 21 also operates to blow the smothering gas into the oxygen feed line when the relay 55 is closed so as to energize its solenoid 45a and thereby vent its diaphragm chamber 42 through valve 44a. After a sufficient delay, to assure extinguishing of the fire, the relay 48 is again closed and the system is once more restored to condition for operation. Only the amount of nitrogen (or other smothering gas) in the pipes and furnace is left in the system. It is readily separated from the product gases, by renewed normal operation. While the fire area is isolated between the closed valves 35, 36 and 14, any excess pressure is vented through the water trap 15; and, advantageously, the nitrogen or other smothering gas is supplied at a pressure sufficient to cause such venting so as to assure purging the apparatus of any burning gas before operation is resumed.

When a backfire or a spontaneous ignition occurs in the mixing chamber 2, the temperature suddenly rises, the increase producing substantially instantaneous response by the temperature-responsive device 16, which automatically initiates the following simultaneous effects by energizing the magnetic circuits and under the action of the solenoid valves:

(1) Closing the shut-off valves 8 and 11 feeding the gaseous reagents, said valves being automatic and rapidly working, advantageously guillotine valves.

(2) Opening the automatic valve 22, thereby blowing in nitrogen and immediately purging conduit 10 downstream from the stop valve.

(3) Opening the automatic valve 20, thereby blowing in nitrogen and purging conduit 7, near the inlet of the mixing chamber, to block the oxygen contained within the conduit 7 from continuing to support combustion.

(4) Closing the automatic valve 14 on the outlet conduit 13 of the pyrolysis gases, immediately downstream from the pyrolysis furnace, said closing forcing the venting of the gases through the safety device 15.

(5) Closing the heating devices of the preheaters 9 and After a previously determined period corresponding to that required for purging all the hydrocarbon circuit downstream the valve 11, plus a margin of safety, the automatic valve 21 feeding nitrogen opens, the nitrogen thus introduced then purging all the oxygen circuit downstream from the valve 8.

Under such circumstances, the extinction of the flame produced in the mixing chamber 2 is substantially instantaneous in such a manner that the detecting thermocouple 16 in the mixing chamber is not damaged.

For controlling the efiiciency of the process of this invention, some twenty premature ignitions of the hydrocarbon to be pyrolyzed have been caused in the mixing chamber 2 and it has been observed that:

(1) The bare thermo-couple was not melted and had not been damaged.

(2) The pre-ignition detection by the thermo-couple was substantially more rapid than with a pressiometer (connected directly on the mixing chamber and detecting a combustion by the pressure difference between the lower part and the upper part of said chamber), provided as an additional safety device.

A variety of temperature-responsive devices are already known which are capable of operating the relay 48 in response to a predetermined high temperature. We have referred to a thermocouple as a particularly advantageous example of such devices, as it is rugged, capable of repeated operation and not destroyed by the temperature to which it responds.

We claim:

1. In the pyrolysis of hydrocarbons by partial combustion, a process for extinguishing undesired pro-ignition flame in a pre-mixing zone adjacent a high-temperature reaction zone in said pyrolysis process continuously fed by flammable gas and a flame supporting gas, which comprises shutting off said pre-mixing and reaction zones from the supplies of said gases fed thereto and from the reacted product gases produced therein, flooding said zones thus shut off with a smothering gas and diverting the flow of gases from said zones through a discharge into the atmosphere.

2. A process as defined in claim 1 in which said shutting off of said zones and said flooding of said smothering gas are automatically responsive to a temperature substantially above normal in said pre-mixing Zone.

3. A process as defined in claim 1 in which said shutting off of said zones and said flooding of said smothering gas are effected by electrically controlled valves and which a thermo-couple in said pre-mixing zone controls the operation of said valves in response to a temperature substantially above normal therein.

4. A process as defined in claim 1 in which said shutting off occurs on both upstream and down-stream sides of said zones and beyond the points adjacent said zones where said gases are hot.

5. In the pyrolysis of hydrocarbons by partial combustion, a process for rapid extinction of flame within a mixing chamber fed by oxygen and hydrocarbon gas preheated to near the flash point of the hydrocarbon in the oxygen which comprises shutting oif the oxygen feed stream at a position upstream of that at which it is heated to said temperature and upstream of that at which it meets the hydrocarbon, blowing nitrogen at higher pressure into the feed stream at a point adajcent to the mixing chamber, whereby oxygen is blocked, replacing the hydrocarbon feed with nitrogen upstream of the means for preheating the hydrocarbon, and venting off flame products and nitrogen downstream from said chamber, whereby nitrogen flows through the mixing chamber.

6. The process according to claim 5 which includes introducing, after a short delay, nitrogen close to and downstream of the point at which the oxygen feed stream is shut off whereby the oxygen theretofore blocked in said stream by the higher pressure nitrogen is flushed from said stream through the mixing chamber by the resulting flow of nitrogen.

7. The process according to claim 5 in which the outlet for the reacted gases from said pyrolysis is shut off immediately when flame is detected in the mixing chamber.

8. The process according to claim 5 which further comprises continually detecting a temperature in the mixing chamber, and automatically initiating said steps of shutting off feed and blowing in smothering gas in response to abnormal temperature rise resulting from ignition of the gases therein.

9. A process as defined in claim 1 in which said shutting off of the feed supply of said flame-supporting gas occurs at a substantial distance upstream from said zones, and in which said smothering gas is blown into said feed supply stream first closely adjacent said zones effecting immediate smothering of said pre-ignition flame in said pro-mixing zone by depriving said flame of further flame-supporting gas and then, after a delay suflicient to smother and extinguish said flame, additional smothering gas is blown into said flame-supporting gas feed stream at a point closer to said shut-off point for purging said feed stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,155,119 Ebner Apr. 18, 1939 2,247,181 Berhoudar June 24, 1941 2,590,436 Luten Mar. 25, 1952 2,784,068 Beggs et al Mar. 5, 1957 2,818,326 Eastman et al Dec. 31, 1957 2,838,585 Lehrer June 10, 1958

Claims (1)

1. IN THE PYROLYSIS OF HYDROCARBONS BY PARTIAL COMBUSION, A PROCESS FOR EXTINGUISHING UNDESIRED PRE-IGNITION FLAME IN A PRE-MIXING ZONE ADJACENT A HIGH-TEMPERATURE REACTION ZONE IN SAID PYROLYSIS PROCESS CONTINUOUSLY FED BY FLAMMABLE GAS AND A FLAME SUPPORTING GAS, WHICH COMPRISES SHUTTING OFF SAID PRE-MIXING AND REACTION ZONES FROM THE SUPPLIES OF SAID GASES FED THERETO AND FROM THE REACTED PRODUCT GASES PRODUCED THEREIN, FLOODING SAID ZONES THUS SHUT OFF WITH A SMOTHERING GAS AND DIVERTING THE FLOW OF

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