METHOD AND APPARATUS FOR INTRODUCING A LIQUID FEED INTO A VAPOR/LIQUID SEPARATION TOWER

Abstract: A flashing feed inlet (1) is used in a distillation column (3), to decrease the amount of liquid entrainment and maldistribution of vapor occurring in the column (3). The inlet (1) comprises: a) a feed pipe (5) containing at least one side opening (9) cut an angle alpha of not greater than about 30 DEG below or above the horizontal axis and at least one opening (13) in the bottom of the feed pipe (5), and b) a flashing chamber (7), connected to, spaced from and surrounding the feed pipe (5), having a sufficient cross-sectional area to decrease the linear velocity of a vapor, produced by flashing of at least a portion of the feed stream in flashing feed inlet (1), to substantially that of the superficial vapor velocity within the column (3), the flashing chamber (7) additionally providing a surface (10) for the feed stream to strike.

Description: METHOD AND APPARATUS FOR INTRODUCING A LIQUID FEED INTO A VAPOR/LIQUID SEPARATION TOWER This invention is directed to a method and apparatus for introducing a liquid feed into a vapor/liquid separation tower. Vapor/liquid separation towers, such as distillation columns, are extensively used in chemical engineering industries. Such a tower will efficiently and effectively separate a feedstock into a number of desired fractions if the feedstock is introduced into the tower at the conditions of temperature and pressure substantially equal to or lower than those prevailing within the column. However, if the temperature and/or pressure of the feedstock introduced into the tower is higher than that prevailing within it, a steady-state upsetting condition known as "flashing" will occur in the column. Flashing vaporizes at least a portion of the feed and produces vapor at a very high velocity, e.g., 50 feet per second (15m/s) , which causes the entrainment of a substantial amount of the liquid portion of the feedstock in the vapor and maldistribution of the vapor. The entrainment of the liquid portion of the feedstock and/or maldistribution of the vapor portion of the feed decrease the efficiency of the separation tower. Heretofore-known devices for promoting a uniform distribution of the feedstock in the tower did not address the problem of flashing of the feedstock. The emphasis has been placed instead on the efficient distribution of the liquid feedstock introduced into the column, while the phenomenon of flashing of the portion of the liquid feedstock into vapor was either not recognized or not addressed by those skilled in the art. It is a primary object of the present invention to provide a method and apparatus for minimizing the adverse effects of flashing experienced upon the introduction of a liquid feed having a higher temperature and/or pressure than those within the separation tower into which the feed is introduced. Accordingly, the invention resides in one aspect in a method of introducing a liquid feed stream into a liquid/vapor separation tower, the feed stream having a temperature and/or pressure higher than those existing in the tower, comprising introducing the feed stream into the tower through a flashing feed inlet whereby at least a portion of the feed stream is converted to a vapor, the feed stream being introduced initially through a feed pipe of said inlet containing at least one side opening cut at an angle ~ * of not greater than 30" below or above the horizontal axis, wherein the angle & _ is defined as an angle between the horizontal axis and the upper edge of the side opening, the side opening having sufficient cross-sectional area to reduce the linear velocity of the feed stream to not less than 3 feet/second (lm/s) , the feed stream exiting the side opening and entering a flashing chamber of the inlet, the flashing chamber being spaced from and surrounding the feed pipe, and the flashing feed inlet decreasing the linear velocity of the vapor to substantially the superficial vapor velocity within the tower. In a further aspect, the invention resides in a flashing feed inlet for introducing a liquid feed stream into a liquid/vapor separation tower, the feed stream having a temperature and/or pressure higher than those existing in the tower, the flashing feed inlet being mounted in the tower perpendicular to the direction of flow of gas and liquid within the tower and comprising: a) a feed pipe containing at least one side opening cut at an angle / of not greater than about 30° below or above the horizontal axis, wherein the angle ©-^ is defined as an angle between the horizontal axis and the upper edge of the side opening, and at least one opening in the bottom of the feed pipe, the total cross-sectional area of the side opening being sufficient to decrease the linear velocity of the feed stream to not less than 3 ft/sec (lm/s) , and b) a flashing chamber, operatively connected to, spaced from and surrounding said feed pipe, having a sufficient cross-sectional area to decrease the linear velocity of a vapor, produced by flashing of at least a portion of the feed stream in the flashing feed inlet, to a value substantially the same as the superficial vapor velocity within the tower, the flashing chamber additionally providing a surface for the feed stream to strike, thereby promoting the separation of the vapor from the liquid. The vapor/liquid separation tower used with the flashing feed inlet of the present invention may be any of the conventional, well-known vapor/liquid separation towers used heretofore to separate a liquid feed stream into a series of distinct liquid and vapor fractions. Suitable separation towers are distillation and gas absorber columns operated over a pressure range from vacuum to very high pressure. The type of the feed stream introduced into the column would depend on the type of material to be separated in the tower, and therefore the nature thereof is not critical to the present invention, so long as the temperature and/or pressure of the feed stream is higher than those existing within the tower. In operation, an existing vapor/liquid contacting tower, such as a distillation column, is modified by incorporating the flashing feed inlet of the present invention within the tower at the inlet thereof. The flashing feed inlet is normally placed in-between two distillation column trays to allow the vapor to rise to the upper tray and the liquid to fall to the lower tray. The device is placed at the same vertical elevation in the column as the conventional feed inlet in the column. The invention will now be more particularly described with reference to the accompanying drawings, in which Figure 1 is a top view of a flashing feed inlet according to one example of the present invention, Figure 2 is a view of Section B-B of Figure 1, and Figure 3 is a view of Section C-C of Figure 1. Referring to the drawings, the flashing feed inlet 1 is positioned within a distillation column 3 so that a liquid feed stream introduced into the column passes through the inlet. The flashing feed inlet 1 comprises a feed pipe 5 which extends perpendicular to the axis of the column 3 from an inlet 6 positioned on the outside of the column to a flashing chamber 7 located within the column. The feed pipe is sized to accommodate the rate of flow of feed streams introduced into the tower, and it is preferably circular in cross-section. The flashing chamber 7 is spaced from and surrounds the feed pipe 5 and is connected thereto by way of a plurality of side slots 9 in the pipe 5. The side slots 9 have a sufficient cross-sectional area to reduce the linear velocity of the feed stream to not less than 3 ft/sec (lm/s) , preferably to 3 to 7 ft/sec (1 to 2 m/s) , thereby minimizing the entrainment of liquid in the vapor ascending within the column. The slots 9 are cut in the feed pipe at such an angle as to promote the impingement of the majority of the liquid portion of the feed onto the side walls of the flash chamber surrounding the feed pipe to minimize the amount of the liquid, if any, travelling upwardly through the distillation column. This, in turn, minimizes the entrainment of the liquid in the vapor. Thus, the angle of the pipe openings (referred to herein as angle C* _ and defined as an angle between the horizontal axis and the upper edge of each opening - see Figure 2) is not greater than about 30" below or above the horizontal axis. The feed pipe also contains two drain holes 13 which allow the liquid to be drained at shutdown from the feed pipe into the flash chamber 7. The cross-sectional area of the flashing chamber 7 is arranged so as to reduce the linear velocity of the vapor produced by flashing to a value approaching the superficial vapor velocity within the tower, thereby separating substantially completely the vapor and the liquid resulting from the flashing of the feed stream. The reduction of the velocity of the vapor to that level reduces the amount of the liquid portion of the feed entrained within the vapor. As shown best in Figure 2, the flashing chamber 7 comprises a semi-circular bottom portion 8 and two sidewalls 10 attached to the bottom portion and terminating in two lip sections 15 which provide structural rigidity and prevent liquid creeping up the inner wall of the device. The flash chamber 7 contains a bottom slot 11 which allows the liquid to exit from the flashing feed inlet and enter one of the lower trays in the distillation column. An end plate 17 closes off the end portion of the pipe 5 and chamber 7 remote from the inlet 6. In one example of operation of the column, the feed stream is introduced outside of the distillation column through the inlet 6 of the feed pipe and it is conducted in a horizontal direction into the distillation column along the length of the feed pipe. The side slots 9 reduce the linear velojcity of the feed stream, comprising both, liquid and vapor, to about 3 ft/sec. (1 m/s) and force the feed to strike the sidewalls 10 which promotes the disengagement of the vapor from the liquid. The vapor portion of the feed stream exits upwardly and is transported to the upper trays of the distillation column. The liquid portion of the feedstream is transported through a bottom slot 11 of the flash chamber 7 to a tray immediately beneath the flashing feed inlet. The flash chamber has such a cross-sectional area that the linear velocity of the vapor portion of the feed stream is reduced to a value approaching the superficial vapor velocity within the tower.

Claims: CLAIMS : 1. A method of introducing a liquid feed stream into a liquid/vapor separation tower, the feed stream having a temperature and/or pressure higher than those existing in the tower, comprising introducing the feed stream into the tower through a flashing feed inlet whereby at least a portion of the feed stream is converted to a vapor, the feed stream being introduced initially through a feed pipe of said inlet containing at least one side opening cut at an angle ^- of not greater than about 30° below or above the horizontal axis, wherein the angle Qxζ ^ is defined as an angle between the horizontal axis and the upper edge of the side opening, the side opening having sufficient cross-sectional area to reduce the linear velocity of the feed stream to not less than 3 feet/second (lm/s) , the feed stream exiting the side opening and entering a flashing chamber of the inlet, the flashing chamber being spaced from and surrounding the feed pipe, and the flashing feed inlet decreasing the linear velocity of the vapor to substantially the superficial vapor velocity within the tower. 2. The method of claim 1 wherein the feed pipe decreases the linear velocity of the feed stream to 3 to 7 ft/sec (1 to 2m/s) . 3. The method of claim 1 wherein the vapor exits the flashing feed inlet and is conducted upwardly to upper trays of the tower. 4. The method of claim 3 wherein the liquid is conducted to a tray immediately beneath the flashing feed inlet. 5. A flashing feed inlet for introducing a liquid feed stream into a liquid/vapor separation tower, the feed stream having a temperature and/or pressure higher than those existing in the tower, the flashing feed inlet being mounted in the tower perpendicular to the direction of flow of gas and liquid within the tower and comprising: a) a feed pipe containing at least one side opening cut at an angle Q> of not greater than about 30° below or above the horizontal axis, wherein the angle QZ is defined as an angle between the horizontal axis and the upper edge of the side opening, and at least one opening in the bottom of the feed pipe, the total cross-sectional area of the side opening being sufficient to decrease the linear velocity of the feed stream to not less than about 3 ft/sec, and b) a flashing chamber, operatively connected to, spaced from and surrounding said feed pipe, having a sufficient cross-sectional area to decrease the linear velocity of a vapor, produced by flashing of at least a portion of the feed stream in the flashing feed inlet, to a value substantially the same as the superficial vapor velocity within the column, the flashing chamber additionally providing a surface for the feed stream to strike, thereby promoting the separation of the vapor from the liquid. 6. A flashing feed inlet means of claim 6 wherein the total cross-sectional area of the side opening of the feed pipe is sufficient to decrease the linear velocity of the feed stream to 3 to 7 ft/sec (1 to 2 m/s) .

Inventors: SILVEY FRANK CLARK, SILVEY, FRANK, CLARK
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1990
Main classification: B01D3
IPC codes: B01D3, B01D45, F22B37