英語翻譯
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.