Study Of The Catalytic Coking Problem Of The Deep-Cut Vacuum Furnace

In recent years, more and more heavier crude oil has been imported. Heavier crude oil has larger proportion of residue oil which is harder to process and will increase refining cost for the refinery plants. How to raise the uproot rate of the crude oil is a key problem facing designers in all the refining field. Applying deep-cut technology to get more straight-run distillate is a major method to tackle the problem which has been increasingly addressed in China.In this thesis, application of the deep-cut technology in the vacuum furnace which is the core device in the atmospheric and vacuum unit was taken into consideration. During the operation of deep-cut vacuum furnace, the furnace outlet temperature will be higher than the oil coking temperature and, thus, could lead to the serious coking of the oil. How to reduce or even avoid oil coking becomes the most important problem of deep-cut vacuum furnace design.The thesis focuses on the three methods of reducing oil coking from two aspects i.e. theory and engineering application. The first method is reasonable tube arrangements by which a uniform temperature distribution with no serious heating points may be achieved and, thus, reducing the possibility of local coking. Several deep-cut vacuum furnaces were simulated and different forms of furnace tube arrangements were analysed and discussed.The second method is reasonable coil tube expanding design by which the most reasonable heating or latent heating balance was searched in order to decrease the possibility of local overheating and, thus, to lower the film temperature and reduce coking. To achieve this, the tube expanding approach is discussed and a concept to use oil temperature as a coking criterion is proposed, which will be helpful for the tube expanding design of vacuum furnaces.The third method is reasonable steam injection by which the turbulence of the medium in the tube can be increased and, thus, reduce the possibility of oil coking. Multiple steam injection methods were simulated and compared and the effects of the steam injection volume and injection place were investigated.In addition, principles about oil coking and decoking are given in detail and the theoretical study and engineering application of the deep-cut technology in vacuum furnace were summarized in this thesis.