Abstract: The physical characteristics and composition of coking and scaling samples in different parts of the spiral wound inlet and outlet heat exchanger in catalytic reforming unit were investigated through experimental and analysis. Furthermore, the main causes of coking and scaling in the heat exchanger were analyzed. The results showed that the coking and scaling samples in the lower header and tube side were mainly composed of hydrocarbons, while the coking and scaling samples in the shell side were mainly composed of catalyst dust. There are certain amounts of ammonium salts in the coking and scaling samples in different parts. The hydrocarbons for coking and scaling in the lower header are mainly heavy oil, while the heavy oil content for coking and scaling in the tube side and shell side is relatively low and the degree of carbonization is high. The molecular weight and aromatic ring number of coking and scaling samples in the lower header, tube side and shell side increase sequentially. To inhibit coking and scaling in spiral wound inlet heat exchanger, the formation of coking and scaling in the lower header should be controlled. The cleaning of spiral wound inlet and outlet heat exchanger should adopt the combination method of mechanical coke removal and chemical cleaning, and ammonium salt corrosion should be prevented during the cleaning process.

Key words: reforming, exchanger, coking and scaling, hydrocarbons, catalyst dust