Abstract: Based on the analysis of advanced FCC technologies, an innovation idea of operating the FCC unit under low contact temperature and high catalyst/oil ratio emerged, finally, FDFCC-Ⅲ process for enhancing propylene yield and producing clean gasoline was developed. The test results of pilot plant showed that thermal cracking reactions were significantly suppressed and catalytic reactions were enhanced in FDFCC-Ⅲ process, thus promoting the transformation of sulfur from feed to cracked gas. The commercial application results of the FCC unit of SINOPEC Changling Company indicated that product slates and product qualities were improved by FDFCC-Ⅲ process significantly. When the heavy oil riser was operated at a catalyst/oil ratio of 9.82 and a riser bottom catalyst temperature of 630 ℃, the yields of LPG and propylene were 26.66% and 10.23%, respectively; the dry gas yield was only 4.33%; as to gasoline the volume content of olefins and sulfur content were 17.7% and 0.032%, respectively.

Key words: catalytic cracking, propylene, dry gas, gasoline stock