Designing CDU Preheating Train Thermally Coupled to DCU through Vacuum Residue Temperature

Crude oil distillation unit (CDU) and Delayed coking unit (DCU) present significant energy consumption in a refinery, given the high flow rates involved on process streams. As refiners are increasing the process of opportunity crudes, heat integration on these units becomes more relevant. Because DCU is essentially a semi-continuous process, heat integration involving its hot streams may impact considerably the CDU operation. However, thermal coupling between CDU and DCU can be explored through the evaluation of adequate DCU feed temperature. By increasing vacuum residue temperature to DCU, the DCU cooling demand increases while CDU cooling demand decreases. As pinch location on each unit is relatively high, little influence on heating demand is expected, unless the pinch is modified by variation on vacuum residue temperature to DCU. Capital costs are supposed to suffer variations as well, especially on DCU, due to the required area to preheat the feed and to cool the product streams. This work presents the evaluation of DCU feed temperature relevance on both CDU and DCU overall costs and utility consumption, considering grassroots designs, based on Pinch Analysis approach. Steam generation on each unit will be investigated for an interval of vacuum residue temperature, in order to evaluate the replacement of cooling water expenditure by steam generation revenue. The paper will also discuss the impact of increasing thermal coupling between units in terms of flexibility. Design considerations due to eventual operation, such as vacuum unit shutdown, will be addressed as well.