A 1.0 Mt/a ethylene plant was modified during its overhaul in 2019 to expand its capacity to 1.1 million tons per year. After capacity expansion, the plant has been continuously operated at high load. The heat exchange capacity of quench water heat exchanger could not meet the production requirements when the temperature of circulating water was high in summer and during the feeding and unloading of cracking furnace. The kettle temperature and top temperature of quench water tower were too high, so that some heavy hydrocarbons and water entered the cracking gas compressor system through the top of the quench water tower, increasing the operating load of the compressor and intensifying the risk of coking in compressor impeller channel. By increasing the heat exchange area of quench water heat exchanger, the problem of insufficient heat exchange capacity of the heat exchanger in summer and during the feeding and unloading of cracking furnace was solved, the operation cycle of the plant was prolonged, and good effect was achieved.