Natural gas pretreatment prior to liquefaction

The pretreatment of natural gas having an elevated pressure and containing moisture and about 1.5% to 3.5% by volume of CO.sub.2 prior to liquefaction of said natural gas which comprises the steps of:

• (a) dehydrating said natural gas;
• (b) partially cooling said natural gas by heat exchange with countercurrent streams of pretreated natural gas and separated CO.sub.2, both said streams being hereinafter identified;
• (c) further cooling said partially cooled natural gas from step (b) by heat exchange with a countercurrent stream of methanol withdrawn from a second flashing separation, hereinafter identified;
• (d) still further cooling said further cooled natural gas from step (c) by heat exchange with said countercurrent streams of pretreated natural gas and separated CO.sub.2 ;
• (e) scrubbing said still further cooled natural gas from step (d) at a pressure of at least 150 psia with cold recycled methanol supplied at a temperature in the range of about -30.degree. F. to -80.degree. F. and containing not more than about 0.7% on a molar basis of absorbed CO.sub.2 at the start of said scrubbing;
• (f) passing the scrubbed gas containing not more than about 1.0% by volume of CO.sub.2 as the aforesaid countercurrent stream of pretreated natural gas in steps (b) and (d);
• (g) passing methanol withdrawn from said scrubbing of step (e) through a pressure-reducing valve to effect a substantial pressure drop and a first flashing separation of absorbed CO.sub.2 from said methanol;
• (h) passing said first flash-separated CO.sub.2 as the aforesaid countercurrent stream of separated CO.sub.2 in steps (b) and (d);
• (i) heating methanol withdrawn from said first flashing separation of step (g) by heat exchange with a countercurrent stream of methanol withdrawn from a third flashing separation, hereinafter identified;
• (j) effecting a second flashing separation of absorbed CO.sub.2 from said heated methanol from said first flashing separation of step (g);
• (k) warming methanol withdrawn from said second flashing separation of step (j) by passage as the aforesaid countercurrent stream in step (c) to effect said third flashing separation of absorbed CO.sub.2 to yield the aforesaid countercurrent stream of methanol from said third flashing separation with a residual CO.sub.2 content of not more than about 0.7% on a molar basis;
• (1) recycling to said scrubbing of step (e) the aforesaid countercurrent stream of methanol from said third flashing separation of step (k) after being chilled by said heat exchange of step (i) with methanol from said first flashing separation of step (g);
• and
• (m) applying external refrigeration to methanol withdrawn from or supplied to said scrubbing of step (e) to maintain the temperature of said recycled methanol supplied to said scrubbing in said range of about -30.degree. F. to -80.degree. F.