GB729652A - Improvements in or relating to process of producing acetylene and an apparatus for carrying out said process - Google Patents

Abstract

<PICT:0729652/IV (b)/1> <PICT:0729652/IV (b)/2> Acetylene is prepared from a normally gaseous hydrocarbon by mixing cool gaseous streams of oxygen and said hydrocarbon, the amount of oxygen in the resulting mixture being less than that required for the complete combustion of the hydrocarbon, heating the resulting mixture in a first elongated confined stream to a temperature in excess of 1200 DEG F., said stream moving at a high linear velocity such that substantial combustion of the hydrocarbon does not occur, then passing the heated stream through an enlarged reaction zone at a high linear velocity less than the linear velocity of the first stream, partially combusting said mixture in said reaction zone at a temperature in excess of 2000 DEG F., the average residence time of the molecules undergoing reaction at the last-mentioned temperature being less than 0.01 second, e.g. between about 0.001 and 0.01 second, quenching the <PICT:0729652/IV (b)/3> <PICT:0729652/IV (b)/4> reaction mixture from the partial combustion and separating acetylene from the quenched reaction mixture. Suitable hydrocarbons which may be used are methane, ethane, propane and natural gas. The first reaction temperature may be between 1200 DEG and about 2000 DEG F., e.g. between about 1600 DEG and about 1900 DEG F. The second reaction temperature may be between 2000 DEG and 3000 DEG F., e.g. between about 2600 DEG and 2950 DEG F. It is preferred to heat the cool mixture of oxygen and hydrocarbon in a furnace comprising a pair of firing chambers, a pair of closely spaced refractory walls separating said firing chambers between which is defined a radiant heating section, and an elongated heating tube is positioned within said heating section through which the gas mixture is passed. The heating tube may be in the form of a coil spaced from the refractory walls of the heating chamber, and means are provided in each of the firing chambers for direct flame-firing the surface of each refractory wall whereby flame impingement of the tube is prevented. In Fig. 1, natural gas is pumped with the aid of pump 12 into an absorber 16 into which an absorber oil such as kerosene is introduced through line 18. At the elevated pressures employed (900 to 1000 pounds per square inch), substantially all the hydrocarbons heavier than methane, e.g. ethane, are absorbed by the oil and pure methane, and the methane is passed through line 22 to a reducing valve 23 where the pressure is reduced to about 200 pounds per square inch. The device 24 contains charcoal to remove lost traces of absorber oil from the methane which is then passed through reducing valve 28 to reduce the pressure to about 100 pounds per square inch. Oxygen or air is introduced through line 36 via control valve 42 and is mixed with the methane in box 46 at a pressure of about 100 pounds per square inch or less in quantities less than that required for complete combustion of the methane, e.g. in the volume ratio of about one of oxygen to two of methane. The mixed gases are then fed through line 50 to a coil 52 in the preheating furnace. The flow rate of the mixed gas is adjusted so that the gas pressure at the outlet of the coil is slightly in excess of atmospheric pressure. The coil may be by-passed through line 54 and valve 56 to introduce cool gas at juncture 59 to provide means for controlling the gas temperature before it passes to the reactor 64. An initiator or promoter for the reaction such as propane, acetaldehyde or acetone may be introduced through line 60 to assist in controlling the combustion. The gases leaving the reactor are fed into the quenching tank 74 through which water flows from pipe 78 to pipe 80, the upper part of the tank being fitted with a tower 76 containing Raschig rings. The gases withdrawn from the tower contain hydrogen, carbon monoxide, carbon dioxide, unreacted methane and acetylene, and are passed under pressure to an acetylene absorber 92 containing an absorber for acetylene, e.g. acetone, acetaldehyde, acetonitrile, nitrobenzene, chlorinated hydrocarbons and polyglycols and their esters. The preheating furnace is shown in Figs. 2 and 3 and consists of a pair of firing chambers 100 and 102 laterally spaced from each other and separated by a pair of spaced refractory walls 104 and 106 between which is defined a narrow radiant heating chamber 108. The heating coil 52 is spaced between the refractory walls 104 and 106. Gas burners 114 are fitted in the firing chambers 100 and 102 and impinge against the walls 104 and 106. The reactor is shown in Fig. 5 and contains a tube 64 which is formed from a highly refractory material such as silicon carbide. The gases from the preheater pass through line 62 and gases leaving the reactor are quenched by means of a converging water spray 72 before passing into the quenching tank 74. The temperature of the tube 64 is recorded at a number of positions T1, T2 and T3 in a thermowell 68. The main body of the reactor comprises refractory bricks 71 and insulation 73. Electrical elements 70 are preferably used to heat the reactor but after initially heating the reactor, the heat of combustion may be sufficient to maintain the reaction temperature. It is preferred that the pressure within the reactor be at about atmospheric pressure or less.