INTEGRATED PROCESS FOR NGL (NATURAL GAS LIQUIDS RECOVERY) AND LNG (LIQUEFACTION OF NATURAL GAS)

摘要

The invention relates to an integrated process and apparatus for liquefaction of natural gas and recovery of natural gas liquids. In particular, the improved process and apparatus reduces the energy consumption of a Liquefied Natural Gas (LNG) unit by using a portion of the already cooled overhead vapor from a fractionation column from an NGL (natural gas liquefaction) unit to, depending upon composition, provide, for example, reflux for fractionation in the NGL unit and/or a cold feed for the LNG unit, or by cooling, within the NGL unit, a residue gas originating from a fractionation column of the NGL unit and using the resultant cooled residue gas to, depending upon composition, provide, for example, reflux/feed for fractionation in the NGL and/or a cold feed for the LNG unit, thereby reducing the energy consumption of the LNG unit and rendering the process more energy-efficient.

主权项

1. A process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising:
cooling a feed stream containing light hydrocarbons in one or more heat exchangers, wherein said feed stream is cooled and partially condensed by indirect heat exchange; introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream which are to be introduced into a fractionation system, said fractionation system comprising (a) a light ends fractionation column and a heavy ends fractionation column, or (b) a demethanizer column; expanding at least a portion of the overhead gaseous stream from the gas/liquid cold separator and introducing said expanded overhead gaseous stream into (a) a lower region of said light ends fractionation column or (b) an upper region of said demethanizer column; introducing at least a portion of the bottoms liquid stream from gas/liquid cold separator into (a) said heavy ends fractionation column at an intermediate point thereof or (b) said demethanizer column at an intermediate point thereof; removing a liquid product stream from the bottom of (a) said heavy ends fractionation column or (b) the bottom of said demethanizer column; removing a overhead gaseous stream from the top of (a) said light ends fractionation column or (b) said demethanizer column, and, if said fractionation system comprises said light ends fractionation column and said heavy ends fractionation column, removing a bottoms liquid stream from a lower region of said light ends fractionation column, and introducing said bottoms liquid stream from said light ends fractionation column into the upper region of said heavy ends fractionation column;wherein
(a) when said fractionation system comprises a light ends fractionation column and a heavy ends fractionation column,
(i) subjecting a first portion of the light ends fractionation column overhead gaseous stream to indirect heat exchange with an overhead gaseous stream removed from the top of said heavy ends fractionation column, whereby said overhead gaseous stream from the top of said heavy ends fractionation column is cooled and partially condensed, and introducing the cooled and partially condensed overhead gaseous stream from the top of said heavy ends fractionation column into the light ends fractionation column;(ii) removing a second portion of the overhead gaseous stream from said light ends fractionation column as a side stream, and subjecting said side stream to indirect heat exchange for further cooling, partially liquefying said side stream via indirect heat exchange;(iii) introducing the partially liquefied side stream into a further separation means, recovering liquid product from said further separation means and introducing the recovered liquid product into the light ends fractionation column as a liquid reflux stream and/or the heavy ends fractionation column as a liquid reflux stream,(iv) recovering an overhead vapor stream from said further separation means, subjecting said overhead vapor stream from said further separation means to indirect heat exchange for additional cooling and partial condensation, and feeding the resultant vapor and condensate to an LNG separator wherein a final LNG liquid product is produced, and(v) recovering an overhead vapor stream from said further separation means, compressing said overhead vapor stream from said further separation means to form a residue gas; or (b) when the fractionation system comprises a light ends fractionation column and a heavy ends fractionation column,
(i) subjecting the light ends fractionation column overhead gaseous stream to indirect heat exchange with an overhead gaseous stream removed from the top of said heavy ends fractionation column, whereby the overhead gaseous stream from the light ends fractionation column Is heated and the overhead gaseous stream from the top of said heavy ends fractionation column is cooled and partially condensed, and introducing the cooled and partially condensed overhead gaseous stream from the top of said heavy ends fractionation column into said light ends fractionation column;(ii) further heating and compressing the overhead gaseous stream from the light ends fractionation column to produce a residue gas;(iii) cooling at least a portion of said residue gas whereby the portion of said residue gas is partially liquefied;(iv) introducing an expanded portion of said partially liquefied residue gas into said light ends fractionation column;(v) expanding another portion of said partially liquefied residue gas and introducing the expanded another portion into a further separation means;(vi) recovering liquid product from said further separation means as LNG liquid product; and(vii) recovering an overhead vapor stream from said further separation means, compressing said overhead vapor stream from said further separation means to form a further residue gas; or (c) when the fractionation system comprises a demethanizer column,
(i) subjecting a first portion of the overhead gaseous stream from said demethanizer column to indirect heat exchange with a stream obtained by combining a portion of the overhead gaseous stream from said gas/liquid cold separator and a portion of said bottoms liquid stream from said gas/liquid cold separator to obtain a residue gas;(ii) removing a second portion of the overhead gaseous from the demethanizer column as a side stream, and partially liquefying said side stream by heat exchange;(v) introducing the partially liquefied side stream into a further separation means, recovering liquid product from said further separation means and introducing the recovered liquid product into said demethanizer column as a liquid reflux stream, and(vi) recovering an overhead vapor stream from said further separation means, subjecting said overhead vapor stream from said further separation means to indirect heat exchange for additional cooling and partial condensation, and removing the resultant condensate as a final LNG liquid product; or (d) when the fractionation system comprises a demethanizer column,
(i) subjecting the demethanizer column overhead gaseous stream to indirect heat exchange with a stream obtained by combining a portion of the overhead gaseous stream from said gas/liquid cold separator and a portion of the bottoms liquid stream from said gas/liquid cold separator;(ii) further heating and compressing the overhead gaseous stream from said demethanizer column to produce a residue gas;(iii) cooling at least a portion of said residue gas whereby the portion of the residue gas is partially liquefied;(iv) introducing the partially liquefied residue gas into a further separation means;(v) recovering liquid product from said further separation means and introducing the recovered liquid product as reflux to the demethanizer column;(vi) recovering an overhead vapor stream from said further separation means, cooling said overhead vapor stream from said further separation means whereby the overhead vapor stream is partially liquefied;(vii) introducing the partially liquefied overhead vapor stream from said further separation means into another further separation means; and(viii) recovering liquid product from said another further separation means and removing the recovered liquid LNG as a final product.