Patent ID: 7458232

Claim:
Method for simultaneously producing treated natural gas, a C 3 + hydrocarbon rich cut and, in at least certain production conditions, an ethane rich stream, from an initial natural gas comprising methane, ethane and C 3 + hydrocarbons, the method comprising the following steps: the initial natural gas is cooled and partially condensed; the cooled natural gas is separated into a liquid stream and a gas stream; the liquid stream is expanded and introduced into a recovery column for recovering the C 2 + hydrocarbons at a first intermediate level; the gas stream is separated into a feed stream for the said column and a reflux stream; the feed stream is expanded in a turbine and introduced into the column at a second intermediate level; the reflux stream is cooled and at least partially condensed and, after expansion, introduced into the column at a third intermediate level; the top stream is recovered from the column to form the treated natural gas, and the bottom stream is recovered from the column to form a C 2 + hydrocarbon rich liquid stream; the said bottom stream is introduced at a feed level of a fractionating column equipped with a top condenser, the top condenser comprising a separator drum producing a liquid fraction, the fractionating column producing the ethane rich stream at the top and the said C 3 + hydrocarbon cut at the bottom; and a primary reflux stream produced in the top condenser is refluxed to the fractionating column; wherein that the ethane rich stream is withdrawn from an intermediate level of the fractionating column located above the said feed level of this column; and in that, for ethane extraction rates lower than a preset threshold, at least one secondary reflux stream is produced from the said top condenser by separation of the liquid fraction into the primary reflux stream and the secondary reflux stream and the said secondary reflux stream produced by separation of the liquid fraction is refluxed to the top of the recovery column.