Apparatus and processes for quenching a pyrolysis furnace effluent are provided. In one embodiment, a hydrocarbon stream comprising gas and oil vapor can be quenched with a first quench water stream to form a mixed vapor-liquid stream. The mixed vapor-liquid stream can be fed to a water quench tower to separate the vapor and liquid. The separated vapor can be further quenched with a second quench water stream in the quench tower to form an overhead vapor product comprising light hydrocarbons. Water and liquid hydrocarbons can be collected from the quench tower in an oil-water separator. The liquid hydrocarbons can be recovered from the oil-water separator. Water can be recovered from the oil-water separator. A portion of the recovered water can be cooled. The cooled water can be recycled to the first and second quench water streams.