(82c) Energy Saving for Steam Cracking Furnaces By Combustion Air Preheating Technology

Cracking furnace energy saving is in the major interest of ethylene plants and petrochemical companies. Combustion air preheating technology for the ethylene cracking furnace burners allows for the recovery of some of the low-level waste heat rejected in the furnace effluent stream. Effective recovery of this low-level heat is challenging because its quality is not high enough to be effectively utilized otherwise and is usually removed by cooling water.

This patented combustion air preheating technology is a high-efficiency heat transfer technology. It is designed based on fully mastering of the furnace operation, the plant heat balance, and the innovative experimental research on furnace. This technology utilizes low-level heat sources, such as low-pressure steam (150 ~ 200 ℃), quench water (60 ~ 90 ℃), and low-pressure condensate (100 ~ 200 ℃), to pre-heat the combustion air to the cracking furnaces, thus reducing total firing duty. As the fuel gas consumption is reduced, less flue gas emission is released to environment. Operation of the built piping network is smooth and does not require additional equipment consuming energy (such as pressurized water pump, induced or forced draft fan, motor, etc.). The built system does not require any automatic control system. Preheater of each burner can be easily switched on and off. The combustion air preheater needs only simple maintenance and its working life is more than 15 years. By 2020, this technology has been applied to 308 ethylene cracking furnaces and other negative-pressure heating furnaces in revamp and grassroot plants in China. It has proven its economic benefit, emission reduction, and flexible and reliable operation.

This paper discusses the fundamentals of the combustion air preheating technology. According to practical experience over many years, the energy saving of adding combustion air preheating system can be significant. Improved energy saving is generally achieved with low-level waste heat at higher temperature. The normal operation of cracking furnace is not substantially affected after air preheaters are added. Case studies will demonstrate the cracking furnace thermal efficiency improvement, fuel reduction benefit, and design features for each project based on the individual heat sources and site conditions.