A combined method for recovering valuable components from petroleum field gas and for stabilizing crude petroleum oil

摘要

PICT:0743560/III/1 In a combined process for extracting butanes and/or higher hydrocarbons from field gases and for stabilizing crude petroleum, wherein the gas is contacted with topped crude oil in an absorption zone and the enriched oil, withdrawn from the absorption zone, is introduced into the column used for stabilizing the crude petroleum, part of the stabilized blend withdrawn from the column is passed to a topping still, the vapours evolved in the topping still are passed countercurrent to the oil in the stabilization column, and the topped oil is used for contacting the gas in the absorption zone. An advantage of the process is that no condensers are necessary. Field gas is passed through line 1 into compressors 2, 3; and the compressed gas is introduced into absorber A, which contains bubble trays. Cool topped oil is introduced through line 5 into the upper part of the absorber. The absorption is carried out at a pressure of about 670 p.s.i.g. Lean gas, comprising largely methane and ethane, is withdrawn from the top of the absorber via back-pressure regulator 65. Enriched oil is withdrawn from the base of the absorber; and is passed via lines 7, 71 to flash drum B at 180 p.s.i.g. where volatile components such as propane are separated from the enriched oil. The vapours released in drum B are conducted via line 10 to compressor 3 and from thence to the absorber in order to recover butane therefrom. The oil, withdrawn from the base of drum B, is passed via line 14 to rectifier C which is maintained at 40 p.s.i.g. The rectifier comprises a stabilization zone 15 and a reabsorption zone 16; and raw crude oil is introduced into the former through line 17. A portion of the raw crude oil is also passed through line 20 into the top of zone 16. Vapours from the head of topping still E are introduced into stabilization zone 15 via line 23; and these strip volatile components from the downflowing oil blend. The vapours leaving the head of zone 15 contain desired as well as undesired fractions; and the purpose of zone 16 is to partially reabsorb the former. Any remaining desired fractions in the gas leaving the top of zone 16 are recovered by passing the gas via line 24 and compressors 2, 3, to absorber A. In cases where it is not desired to recover a substantial amount of butane, and a demand for relatively low-pressure fuel gas exists, all of the raw crude oil is fed to zone 15 and topped oil is employed as reabsorption medium in zone 16. The required fuel gas would then be withdrawn via line 30. Partially stabilized blend withdrawn from the base of zone 15 is passed via line 32 into drum D, for removal of salt water, which is discharged through line 35. The oil, freed from water, is now passed via line 37 to heat exchanger H, wherein the temperature is raised from 180 DEG F. to 210 DEG F. The oil then flows through line 38 into the head-section of topping still E, which is also maintained at 40 p.s.i.g. Volatile components are flashed off from the oil in the head of still E; and fully stabilized oil is thereby obtained, a portion of which is withdrawn as product via line 39 and cooler J. The remainder of the stabilized oil flows down through the bubble-cap trays of still E in countercurrent to rising vapours; these vapours being formed by circulating the oil, via lines 48 and 50, through gas-fired heater F., wherein it is heated to 540 DEG F. The "topped" vapours unite with the "flashed" vapours in the head of the still; and the mixture is passed to stabilization zone 15 via line 23. Still E is divided into two zones 43, 44; the downflowing oil being withdrawn from the base of zone 43 via line 45, passed through heat exchanger G, and introduced into the top of zone 44 via line 47. The partially topped oil is heated from 300 DEG to 390 DEG F., while in heat exchanger G, by fully topped oil withdrawn from the base of still E through line 54. The supply of fuel-gas to heater F, and the topping effect, is controlled by controller 51 which is actuated by thermal element 52 immersed in the topped oil in the base of the still. After passing through heat exchanger G, the topped oil traverses heat exchanger H. A by-pass line 61 is provided around heat exchanger G, with a motor valve 62 controlled by controller 63 and thermostat 64 located in line 38. This control mechanism permits the temperature of the stabilized oil entering the head of still E to be controlled by adjusting the temperature of the topped oil sent to heat exchanger H, this adjustment being achieved through by-passing a regulated amount of the topped oil around heat exchanger G. From heat exchanger H, the partially cooled topped oil is conducted via line 56 to heat exchanger H1 wherein it is further cooled by a stream of partially stabilized oil withdrawn from and returned to an intermediate tray of the stabilizing zone via lines 57 and 59. The topped oil is finally cooled with water in cooler I, and is then returned to absorber A via line 5.