Why is the one-pass coke yield simulated by petroSIM for coking units higher than that in the cyclic mode?

When using PetroSIM to simulate coking units, the coke yield in the one-pass mode is higher than that in the cyclic mode. The main reasons are as follows: 1. **Difference in reaction depth of feedstock:** In the one-pass mode, the heavy components enter the coke tower only once, remaining there for a longer time and undergoing greater degree of cracking, which results in an increased coke yield. 2. **Impact of circulating oil properties:** In the circulation mode, a portion of the heavy oil after reaction is returned to the system. The mixture of this circulating stream with the fresh feed alters the properties of the overall feed, resulting in a feed that is relatively lighter and more prone to cracking. This slows down the coking reaction, thereby reducing the yield of coke. 3. **Thermal history effect:** In cyclic operation, certain reformed components undergo thermal cracking multiple times, which is equivalent to partial cracking taking place in advance. As a result, further cracking reactions into coke after entering the coke tower are reduced, leading to a lower yield of coke. In summary, one-pass material pyrolysis is more thorough, resulting in a significantly higher coke yield compared to the cyclic mode; this also explains the significant differences in the properties of the recycled oil and the coke yield observed in the PetroSIM simulation results. .