Publisher Summary This chapter focuses on flowsheets, which is used by an engineer to describe a process, show how its equipments are interconnected, and show the process flows and operatingconditions. Block flowsheets provide an overview of a complex process or plant, with a drawing made with rectangular blocks to represent individual processes or groups of operations, together with quantities and other pertinent properties of key streams between the blocks and into and from the process as a whole. Such block flowsheets are made at the beginning of a process design for orientation purposes or later as a summary of the material balance of the process. Process flowsheets embody the material and energy balances and include the sizes of major equipment of the plant. They include all vessels, such as reactors, separators, and drums; special processing equipment; heat exchangers; and pumps. Numerical data include flow quantities, compositions, pressures, and temperatures. Piping and instrument (P&ID) diagrams do not show operating conditions or compositions or flow quantities, but they show all major as well as minor equipment more realistically than on the process flowsheet. They include the sizes and specification classes of all pipelines, all valves, and all instruments. In fact, every mechanical aspect of the plant regarding the process equipment and their interconnections is represented except for supporting structures and foundations. Utility flowsheets are used for individual utilities such as steam, steam condensate, cooling water, heat transfer media in general, compressed air, fuel, refrigerants, and inert blanketing gases, and how they are piped up to the process equipment.