Discussion on heating and pressurization issues during startup and shutdown of diesel upgrading units
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During the start-up of diesel upgrading, should the temperature and pressure be increased first, or the pressure first and then the temperature? During startup, the pressure rises to the operating pressure with a large cycle volume, so isn’t the rate of temperature increase fast? Also, during the shutdown process, should the pressure be reduced first and then the temperature, or vice versa?
During the shutdown process, should the pressure be reduced first and then the temperature, or should the temperature be lowered first and then the pressure?
Cool down first; if the pressure drops first, hydrogen cannot be completely removed from the pump outlet
First raise the temperature to a certain level before increasing the pressure
To what temperature does the temperature rise during startup before voltage is increased?
Until the lowest temperature of the bed layer reaches 135°C, the reaction pressure shall not exceed 3.0 MPa
Do you mean diesel upgrading as in diesel hydroprocessing? If so, for all hydroprocessing units, pressure must be increased first, followed by an increase in temperature. The pressure that can be applied depends on the material used for the high-pressure components; hydrogenation units generally use molybdenum-based steels, which require higher temperatures in order to withstand greater pressures. To prevent embrittlement of these molybdenum-based steels due to tempering, the pressure is usually kept below 3.5 MPa. Then start the circulation pump, ignite it to raise the temperature; once the temperature exceeds that at which temper brittleness occurs, continue to increase the pressure until the operating pressure is reached. As for during shutdowns, cooling and pressure reduction must also follow this principle. But the temperature can be lowered first, followed by reducing the pressure. On the one hand, it facilitates dehydrogenation; on the other hand, the higher pressure helps with cooling.
During startup, the temperature should be increased first before raising the pressure. Until the temperature of the reactor walls does not exceed 93 degrees, the pressure must not exceed one-third of the operating pressure; this is related to the austenite temper brittleness of the reactor material. Once the temperature exceeds 93 degrees, both pressure and temperature can be increased simultaneously. During shutdown, the temperature should be reduced first, while the pressure can remain unchanged. A higher pressure results in a larger volume of steam circulation, which helps to lower the temperature more quickly, as well as reducing the time during which hot hydrogen is in contact with oil