Issues regarding low-load diesel hydrotreating in the early stage of diesel hydrocracking
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I would like to ask the experts: Suppose a facility is ultimately intended to be designed for diesel hydrocracking at a capacity of 1 million tons per year. However, due to certain reasons, it must first be put into operation for diesel hydrotreating at a capacity of 500,000 tons per year, with the plan to later convert it into a facility for diesel hydrocracking at 1 million tons per year. As a result, large-scale equipment such as reactors and distillation towers must be designed and constructed for a processing capacity of 1 million tons per year, so that they can be modified later as needed. I would like to ask whether this plan is feasible? What problems might arise? If the distillation tower is designed on a large scale, with the openings in its walls arranged according to the requirements of a 1 million-ton diesel cracking unit, and those that are not needed in the initial stage of 500,000-ton diesel refining are temporarily sealed off, then can the distillation requirements for a processing capacity of 500,000 tons per year be met under such low-load conditions by adjusting factors such as the opening ratio of the tray plates? What are the things to keep in mind during design and construction, and are there any other issues?
For your reference, the previous unit had issues with operating at ultra-low load. The extremely low operating speed of the unit under ultra-low load leads to an uneven temperature distribution in the bed; this creates a risk of hot spots and channeling over time. Excessive load on the hydrogen circulation machine (turbine) results in high temperatures in the bed, thereby increasing the unit’s energy consumption ； There is a cold air bypass in the distillation system ； Insufficient heat absorption for stabilization ； Overall, the control valves are not suitable for low-load operating conditions, resulting in an **increase in operational load. If conditions permit, it is best to achieve full circulation of the residual oil to reduce bottom pressure and thereby increase heat extraction. The openings and extraction in the distillation tower are not the main problems.