ABSTRACT
For example, in a simplified process for vacuum gas oil desulfurization (Fig. 17.23), the vacuum gas oil feedstock is mixed with hydrogen makeup gas and preheated against reactor effluent. Further preheating to reaction temperature is accomplished in a tired heater. The hot feed is mixed with recycle gas before entering the reactor. The temperature rises across the reactor owing to the exothermic heat of reaction. Catalyst bed temperatures are usually controlled by using multiple catalyst beds and
Table 17.12 Vacuum Gas Oil Hydrodesulfurization and Mild Hydrocracking Process Data
VGO HDS
MHC
by introducing recycle gas as an interbed quench medium. Reactor effluent is cooled against incoming feed and air or water before entering the high pressure separator. Vapors from this separator are scrubbed to remove hydrogen sulfide (H2S) before compression back to the reactor as recycle and quench. A small portion of these gases is purged to fuel gas to prevent buildup of light ends. Liquid from the high pressure separator is flashed into the low pressure separator. Sour flash vapors are purged from the unit. Liquid is preheated against stripper bottoms and in a feed heater before steam stripping in a stabilizer tower. W<jcter wash facilities are provided upstream of the last reactor effluent cooler to remove ammonium salts produced by denitrogenation of the vacuum gas oil feedstock.
