Fig.1. Flow scheme of a very simple

Fig.1. Flow scheme of a very simple refineryThe next stage of complexity is often to add a desulphurization unit to treat the diesel fuel. This much widens the range of crude oils available to the refinery to process, since few crude oils give suitable diesel fuel by distillation alone: this will lower the real cost of crude oil to the refinery. Usually also the growing refinery will be called upon to make liquefied petroleum gases (LPG). These stages add the desulphurization unit to the refinery, and a more elaborate distillation of the crude oil needed to make propane and butane as new streams. The derosine may also, perhaps, need desulphurizing, unless one again restricts the choice of crude oils. The refinery flow scheme then becomes rather more complex as shown in Fig. 2. Such a refinery is referred to as a simple ‘Hydroskimming’ Refinery commonplace in many areas, e.g. in Europe up to the late 1960s to 1970s. (For this reason the ‘hydroskimming’ refinery scheme will be taken as the ‘base case’ in considering, in Chapter Ⅱ on Future Refinery Trends, the various types of yield enhancements currently being selected in order to meet the refining demands both of the present day and for the future.)As the need develops to produce speciality products such as bitumens, lubes, waxes, etc., and to increase the yield of premium products such as motor gasoline above that simply obtainable from crude, many more units will be added, and a large and complex refinery will have some of all of the following: