A technology is developed for combined pyrolysis of liquefied hydrocarbon gases (LHG) and recycled ethane in separate pyrolysis coils of the same furnace. This technology is desirable when the ethylene production capacity is increased. Comparing the results of the combined pyrolysis of ethane and LHG and their pyrolysis in separate pyrolysis coils showed that ethane must be pyrolyzed separately. The operational regime parameters of the furnace that optimize ethane conversion and the ethylene and propylene yields from ethane and LHG pyrolysis in separate pyrolysis coils are presented.