Steam-cracking of modified naphtha

Method for controlling a steam cracker, said method comprising:

• the supply to a steam cracker of steam and of a feedstock of hydrocarbons comprising 5 to 95% by weight of a paraffinic naphtha and 95% to 5% by weight of a mixture of a first component, that is, a gasoline produced by a fluidized bed catalytic cracking (FCC) unit and of a second component comprising at least a hydrocarbon refinery gas and at least a feedstock rich in paraffins, the paraffinic naphtha having from 10 to 60% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 35% by weight of naphthalenes, from 0 to 1% by weight of olefins and from 0 to 20% by weight of aromatics, the FCC gasoline being an unhydrogenated gasoline having from 0 to 30% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 80% by weight of naphthalenes, from 5 to 80% by weight of olefins and from 0 to 60% by weight of aromatics, the refinery gas having from 0 to 5% by weight of hydrogen, from 0 to 40% by weight of methane, from 0 to 50% by weight-of ethylene;
• from 0 to-80% by weight of ethane, from 0 to 50% by weight of propylene, from 0 to 80% by weight of propane and from 0 to 30% by weight of butanes, and the feedstock rich in paraffins containing at least 50% by weight of saturated hydrocarbons, said feedstock containing at least propane or butane;
• and the continuous control of the supply of paraffinic naphtha, of the second component and of the gasoline in the feedstock, in order to obtain an effluent having a desired target composition.

Instrumentation for controlling a steam cracker, said instrumentation comprising:

• means of supplying to a steam cracker steam and a feedstock of hydrocarbons having 5 to 95% by weight of a paraffinic naphtha and 95% to 5% by weight of a mixture of a first component, that is, a gasoline produced by a fluidized bed catalytic cracking (FCC) unit and a second component comprising at least a hydrocarbon refinery gas and at least a feedstock rich in paraffins, the paraffinic naphtha having from 10 to 60% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 35% by weight of naphthalenes, from 0 to 1% by weight of olefins and from 0 to 20% by weight of aromatics, the FCC gasoline being an unhydrogenated gasoline having from 0 to 30% by weight of n-paraffins, from 10 to 60% by weight of isoparaffins, from 0 to 80% by weight of naphthalenes, from 5 to 80% by weight of olefins and from 0 to 60% by weight of aromatics, the refinery gas having from 0 to 5% by weight of hydrogen, from 0 to 40% by weight of methane, from 0 to 50% by weight of ethylene, from 0 to 80% by weight of ethane, from 0 to 50% by weight of propylene, from 0 to 80% by weight of propane and from 0 to 30% by weight of butanes, and the feedstock rich in paraffins containing at least 50% by weight of saturated hydrocarbons, said feedstock containing at least propane or butane;
• and means for continuously controlling the supply of the paraffinic naphtha, of the second component, and of the gasoline in the feedstock, in order to obtain an effluent with a desired target composition.