What are the reasons for the high dry gas volume in high-pressure hydrocracking?
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Recently, in the hydrocracking unit where I work, the cracking temperature had to be increased due to a high BMCI value of the tail oil; the average temperature of the cracking bed reached 383 degrees. However, the BMCI value of the tail oil did not decrease, and the amount of dry gas remained high. The pressure in the absorption and desorption towers was 0.08 MPa higher than the normal operating pressure, and it was not possible to control this pressure without venting. The reasons for this were attributed to the use of Iranian heavy oil as feedstock for the vacuum distillation unit, as well as the poor selectivity of the catalysts used. In order to reduce the tower pressure, the average temperature of the cracking bed was lowered to 371 degrees, and the reaction feed rate was reduced from 248 T/h to 220 T/h. Yet, the amount of dry gas still remained high, staying at its maximum level. I would like everyone to help analyze what other factors could cause a high volume of dry gas
According to what you said, the aromatic index of your tail gas is on the high side. There is no problem with raising the temperature, but this value doesn’t decrease at all, and the amount of dry gas is quite high. I believe the main reason for this is related to the catalyst’s performance; there is a possibility of excessive cracking. Poor catalyst selectivity is another factor as well. It is recommended that you provide the relevant data to the catalyst supplier for assistance!