Ammonium chloride corrosion in the reactor effluent system remains to be a barrier for the safe operation of the ebullated-bed hydrogenation unit as impurity content is higher compared with that of the ordinary hydrogenation units.In this research,a Sinopec envisaged case study was conducted on feed oil containing 2.92 μg/g of Cl and 0.38％of N,because the impurity content of feed oil was representative in residue oil.The deposition patterns in heat exchangers were investigated by changing process variables,and then water wash strategy was optimized in view of the relative humidity to obtain a minimum water flowrate,and finally the process optimization suggestions concerning the operation of heat exchangers were proposed.Results show that with the measured content of nitrogen and chlorine in the feed,the NH4C1 deposition temperature of hot high-pressure vapor and hot low-pressure vapor was 223.4 ℃ and 173.7 ℃,respectively,and the minimum water wash flowrate for heat exchangers of hot high-pressure vapor with mixed hydrogen and hot low-pressure vapor with cold low-pressure oil was 38.0 t/h and 5.4 t/h,respectively.Water wash should be carried out intermittently upstream of the heat exchanger tube passes.In consideration of energy consumption,it is recommended to reduce the tube pass outlet temperature of the above heat exchangers to 240 ℃ and 190 ℃,respectively.