化工专业英语翻译，谢谢

The unit operations are as applicable to many physical processes as to chemical ones. Forexample, the process used to manufacture common salt consists of the following sequence of the unit operations: transportation of solids and liquids, transfer of heat, evaporation, crystallization, drying, and screening. No chemical reaction appears in these steps. On the other hand, the cracking of petroleum8, with or without the aid of a catalyst, is a typical-chemical reaction conducted on an enormous scale. Here the unit operations — transportation of fluids and solids, distillation, and various mechanical separations — are vital, and the cracking reaction could not be utilized without them. The chemical steps themselves are conducted by controlling the flow of material and energy to and from the reaction zone.