Abstract: At one RDS unit in a refinery , following extended operation beyond the design cycle and partial catalyst change-out, the HDS, CCR removal, and HDM performance of the catalyst after unit startupwas lower than expected. To check whether high-pressure heat exchanger (residue feed/reactor effluent) was leak, the resid feed was switched to 100% high-sulfur VGO feed under normal operating condition. Based on the evaluation of sulfur content and sulfur distribution in the resid product, it was successfully confirmed that there was no internal leakage in the high-pressure heat exchanger. This avoided the shutdown of the RDS unit and the inspection process of opening the high-pressure heat exchanger, ensured the online rate of the unit.

Key words: RDS, high-pressure heat exchanger, internal leakage, gas oil, reaction product oil, sulfur content