Slag quenching method for pyrolysis furnaces

In a process for quenching molten residue discharged from a furnace hearth, through a non-submerged taphole, including the steps of:

• (a) providing a vertical slag duct communicating in a sealed manner at the top thereof with said taphole, and sealed at the bottom by being immersed a substantial distance into water in a quench tank, (b) flowing the molten residue from the hearth by gravity to and then down the central axis of said slag duct and quenching said residue in the water contained in the submerged portion of said slag duct, said water being at a temperature sufficiently high to prevent slag explosions, the improvement comprising:
• substantially reducing cooling of the tap and hearth areas of said furnace by (1) removing sufficient hot fluid from said duct generated by quenching of said molten residue in the water contained in the submerged portion of said duct and (2) replacing said removed hot fluid with cooler water, thereby maintaining the temperature of the water in said duct between about 150.degree. F. and the boiling point of the water and substantially preventing steam from entering said tap and hearth areas.