Crude oil distillation

The crude oil distillation systems, with the distillation columns and their heat recovery systems, comes under the first stage of processing in a petroleum refinery. It is an energy intensive process, that consumes fuels at an equivalent of 1% to 2% of the crude oil processed . As the price of energy increases, there must be a reduction in the energy requirement of the crude oil distillation process. At the same time, the environmental problems have resulted in stricter regulations on the emission of green house gases. Consequently, both economic and environmental issues are an important factor in the design of crude oil distillation system. In the crude oil distillation systems, the distillation columns have an interaction with the associated heat recovery systems. In Comparison to the conventional design approach of crude oil distillation systems, the heat-integrated design approach finds a better solution, from which the minimized energy consumption can be obtained. Less energy consumption also means less gas emissions, which is again beneficial for the environment. The heat-integrated design approach is supported by shortcut column models and the pinch analysis method. In order to apply shortcut column models, product specifications in the refineries have to be translated into specifications required by shortcut column models. But there are a lot of limitations present in the existing translation met The crude oil distillation systems contain distillation columns and heat recovery systems (i.e. heat exchanger networks). Usually , the design of distillation columns and the design of heat recovery systems are carried out in a sequential manner. This sequential design approach may miss energy-saving opportunities, and as such several research has been carried out on the heat integrated design approach, which considers the design of distillation columns and their heat recovery systems simultaneously.

The importance of heat-integrated design of crude oil distillation systems has always been a topic of discussion. Several shortcut column models have been applied to develop a heat-integrated design methodology. The reason for using shortcut models is that they are simpler and more robust, compared to rigorous column models .The models and constraints are then incorporated into an optimization framework, that allows the design variables to be optimized in order to minimize the total annualized cost. The major components of the optimization framework are the simulations of crude oil and gas distillation columns and the heat exchanger networks (HEN). In order to optimize the design of crude oil distillation systems, the distillation column and the HEN have to be simulated first. For grassroots design, an initial feasible design is required; while for retrofit design, the existing units are simulated. After the simulations are established, they are then included in the optimization, which aims to minimize the total annualized cost or maximize profit. During the optimization, the column design parameters tend to become adjustable variables, e.g. preheat crude feed temperature, pump-around flow rates; some configuration parameters of the HEN can also become adjustable variables, e.g. adding or removing an exchanger, or re-sequencing an exchanger. The optimization also takes account of constraints such as product quality in terms of boiling points and flow rates and column hydraulic constraints .The reason for adopting shortcut column models is that they are simple and robust, and provides a good preliminary design for the distillation columns. Moreover, applying shortcut column models can allow many important design variables to be optimized simultaneously, which may provide more opportunities to find better design solutions. However, rigorous column models may involve significant convergence problems when many variables are optimized at the same time.