Hydrocarbon gas processing

In a process for separating a feed gas into a volatile residue gas and a relatively less volatile fraction, said feed gas containing hydrocarbons, methane and ethane together comprising the major portion of said feed gas, wherein said gas under pressure is cooled sufficiently to form a liquid portion under pressure and a vapor portion under pressure, and

• (i) said vapor portion under pressure is expanded to a lower pressure, whereby it partially condenses;
• (ii) said liquid portion under pressure is expanded to said lower pressure, whereby a part of said liquid portion vaporizes to cool the expanded liquid portion;
• and
• (iii) at least the liquid formed upon partial condensation after expansion of the vapor portion in step (i) and the liquid remaining after expansion of the liquid portion in step (ii) are supplied to a fractionation column, wherein said relatively less volatile fraction is separated,
• the improvement wherein
• (a) at least some of said liquid portion under pressure is cooled to a temperature below its bubble point prior to expansion thereof,
• (b) at least part of said subcooled liquid portion is expanded to said lower pressure, whereby it is partially vaporized to cool said expanded liquid portion,
• (c) at least part of the liquid remaining in the expanded liquid portion is supplied to said distillation column at a first feed position, and
• (d) at least part of the stream resulting from expansion of said vapor in step (i) is supplied to said fractionation column at a second feed position, said second feed position being in a lower column position than said first feed position.

In an apparatus for separating a feed gas into a volatile residue gas and a relatively less volatile fraction, said feed gas containing hydrocarbons, methane and ethane together comprising the major portion of said feed gas, said apparatus including

• (i) a first cooling means to receive said feed gas under pressure and to cool it sufficiently to form a liquid portion and a vapor portion,
• (ii) a separation means connected to said first cooling means to separate said liquid portion under pressure and said vapor portion under pressure,
• (iii) first expansion means connected to the separation means to receive said vapor portion under pressure and expand it to a lower pressure, thereby partially condensing said expanded vapor stream,
• (iv) a second expansion means connected to receive said liquid portion under pressure and to expand said liquid portion to said lower pressure, thereby to vaporize a portion of said liquid and to cool the expanded liquid portion, and
• (v) a fractionation means connected to said first and second expansion means to receive at least the liquid formed from partial condensation of said expanded vapor and the liquid remaining from expansion of said liquid stream, to separate said relatively less volatile fraction,
• the improvement comprising
• (a) a subcooling means connected intermediate said separation means and said second expansion means to cool said liquid portion under pressure to a temperature below its bubble point prior to expansion thereof, said subcooling means being connected to supply at least a portion of said subcooled liquid to said second expansion means, and
• (b) said second expansion means is connected to supply at least part of the liquid remaining in the expanded subcooled liquid portion to said distillation column as a top liquid feed thereto.

In an apparatus for separating a feed gas into a volatile residue gas and a relatively less volatile fraction, said feed gas containing hydrocarbons, methane and ethane together comprising the major portion of said feed gas, said apparatus including

• (i) a first cooling means to receive said feed gas under pressure and to cool it sufficiently to form a liquid portion and a vapor portion,
• (ii) separation means connected to said cooling means to separate said liquid portion under pressure and said vapor portion under pressure,
• (iii) a first expansion means connected to said separation means to receive said vapor portion under pressure and expand it to a lower pressure, thereby partially condensing said expanded vapor portion,
• (iv) a second expansion means connected to receive said liquid portion under pressure and to expand said liquid portion to said lower pressure, thereby to vaporize a portion of said liquid and to cool the expanded liquid portion, and
• (v) a fractionation means connected to said first and second expansion means to receive at least the liquid formed from partial condensation of said expanded vapor and the liquid remaining from expansion of said liquid stream to separate said relatively less volatile fraction,
• the improvement comprising
• (a) a subcooling means connected intermediate said separation means and said second expansion means to cool said liquid portion under pressure to a temperature below its bubble point prior to expansion thereof, said second cooling means being connected to supply at least a portion of said subcooled liquid to said second expansion means,
• (b) said second expansion means being connected to supply at least a part of the liquid remaining in the expanded subcooled liquid portion to said distillation column at a first column feed position, and
• (c) said first expansion means being connected to provide at least a part of the expanded vapor stream to said fractionation column at a second feed position, said second feed position being in a lower column position than said first feed position.