Patent TW-426665-B (TW)
Title: Aromatics and/or heavies removal from a methane-based feed by condensation and stripping
Inventor: DEVERS BERNARD J
IPC: F25J3/02
Filed: 1997-05-22
Granted: 2001-03-21
Abstract: A process for removing and concentrating the higher molecular weight hydrocarbon species from a methane-based gas stream comprising the steps of: (a) condensing a minor portion of the methane-based gas stream thereby producing a two-phase stream; (b) feeding said two-phase stream into the upper section of a column; (c) removing from the upper section of said column a heavies-depleted gas stream; (d) removing from the lower section of said column a heavies-rich liquid stream; (e) contacting via indirect heat exchange the heavies-rich liquid stream with a methane-rich stripping gas stream thereby producing a warmed heavies-rich stream and a cooled methane-rich stripping gas stream; (f) feeding said cooled methane-rich stripping gas stream to the lower section of the column; and (g) contacting the two-phase stream and the cooled methane-rich stripping gas stream in said column thereby producing the heavies-depleted gas stream and the heavies-rich liquid stream. A process for removing benzene and other aromatics from a methane-based gas stream comprising the steps of: (a) condensing a minor portion of the methane-based gas stream thereby producing a two-phase stream; (b) feeding said two-phase stream into the upper section of a column; (c) removing from the upper section of said column a benzene/aromatic-depleted gas stream; (d) removing from the lower section of said column a benzene/aromatic-rich liquid stream; (e) contacting via indirect heat exchange the benzene/aromatic-rich liquid stream with a methane-rich stripping gas stream thereby producing a warmed benzene/aromatic-rich stream and a cooled methane-rich stripping gas stream; (f) feeding said cooled methane-rich stripping gas stream to the lower section of the column; and (g) contacting the two-phase stream and the cooled methane-rich stripping gas stream in said column thereby producing the benzene/aromatic-depleted gas stream and the benzene/aromatic-rich liquid stream. An apparatus for removing and concentrating the high molecular weight hydrocarbon species from a methane-based gas stream comprising: (a) a condenser; (b) a column for stripping out the lighter components of the liquid phase of a two phase liquid gas methane stream using a cooled methane rich stripping gas; (c) a heat exchanger providing for indirect heat exchange between two fluids; (d) a conduit between said condenser and the upper section of the column for flow of a two-phase stream to the column; (e) a second conduit connected to the upper section of the column for the removal of a vapor stream from the column; (f) a conduit between said column and heat exchanger for flow of a cooled gas stream from the heat exchanger; (g) a conduit between said column and said heat exchanger for flow of a liquid stream from the column; (h) a conduit connected to the heat exchanger for flow of a warmed liquid stream form the heat exchanger; and (i) a conduit connect to the heat exchanger for flow of a gas stream to the heat exchange. An apparatus for providing heat exchanger controls separation column comprising: (a) a cryogenic separation column for partially condensing a feed gas stream in an LNG recovery process; (b) means for withdrawing a liquid condensate stream from said cryogenic separation column; (c) a heat exchanger associated with said cryogenic separation column; (d) means for passing a warm dry gas stream through said heat exchanger and thereafter to said cryogenic separation column, wherein said warm dry gas stream is cooled by indirect heat exchange with said liquid condensate stream in said heat exchanger, (f) a bypass conduit having a first control valve operably located therein for bypassing said warm dry gas stream around said heat exchanger; (g) means for establishing a first signal representative of the actual temperature of said warm dry gas stream exiting said heat exchanger; (h) means for establishing a second signal representative of the actual temperature of said liquid condensate stream entering said heat exchanger; (i) means for dividing said first signal by said second signal to establish a third signal representative of the ratio of said first signal and said second signal; (j) means for establishing a fourth signal representative of a desired value for the ratio represented by said third signal; (k) means for comparing said third signal and said fourth signal and establishing a fifth signal which is responsive to the difference of said third signal and said fourth signal, wherein said fifth signal is scaled to be representative of the position of said first control valve required to maintain the actual ratio represented by said third signal substantially equal to the desired ratio represented by said fourth signal; and (m) means for manipulating said first control valve in said bypass conduit in response to said fifth signal. A method for controlling temperature in a heat exchanger equipped with a bypass conduit having a first control valve operatively connected therein, said heat exchanger being associated with a cryogenic separation column that removes a benzene contaminant from a feed stream in and LNG recovery process, said method comprising: withdrawing a liquid condensate stream at a cryogenic temperature from said cryogenic separation column; passing said liquid condensate stream through said heat exchanger; passing a warm dry gas stream through said heat exchanger and thereafter introducing said warm dry gas stream into said cryogenic separation column, wherein said warm dry gas stream is cooled by indirect heat exchange with said liquid condensate stream in said heat exchanger, establishing a first signal representative of the actual temperature of said warm dry gas stream exiting said heat exchanger; establishing a second signal representative of the actual temperature of said liquid condensate stream entering said heat exchanger; dividing said first signal by said second signal to establish a third signal representative of the ratio of said first signal and said second signal; establishing a fourth signal representative of a desired value for said third signal; comparing said third signal and said fourth signal and establishing a fifth signal which is responsive to the difference between said third signal and said fourth signal, wherein said fifth signal is scaled to be representative of the position of said first control valve required to maintain the actual ratio represented by said third signal substantially equal to the desired ratio represented by said fourth signal; and manipulating said first control valve in said bypass conduit in response to said fifth signal.