The delayed coking process comprises the steps of: thermally cracking hydrocarbon feedstock in the coke drum thereby converting the feedstock to coke and hydrocarbon products; routing thermally crack hydrocarbon products to downstream fractionators; and periodically removing coke out of the drum. Before coke removal, the drum has to be steam stripped, water quench, then vented. During venting, H2S scavenger is injected to the drum vapor space to remove residual H2S.