The alkali preheater is a key equipment for improving energy efficiency in caustic soda evaporation. Previously, plate heat exchangers with high heat exchange efficiency and small volume were used. However, due to working conditions, the sealing gasket of the plate heat exchanger was easily damaged, causing leakage and affecting the continuity of production. After long-term on-site analysis, our company has adopted a nickel twisted tube multi pass series tube heat exchanger, which overcomes the problem of lower heat transfer efficiency of tube heat exchangers compared to plate heat exchangers, greatly improving the service life and maintenance frequency of the equipment. The equipment produced by our company has been running continuously for 5 years without any leakage. It is divided into alkali alkali preheater and alkali and steam condensate preheater.