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To reduce detailed written descriptions on flowsheets, it is usual practice to develop or adopt a set of symbols and codes, which suit the purpose. Flowsheet symbol standardization has been developed by various professional and technical organizations for their particular fields. The American National Standard Institute (ANSI) has also adopted most of these symbols. The following symbols references are related and useful for many chemical and mechanical processes:

1 1. American National Standard Institute (ANSI) (www.ansi.org)

2 2. American Institute of Chemical Engineers (AIChE) (www.aiche.org)(a) Letter Symbols for Chemical Engineering, ANSI Y10.12

3 3. American Society of Mechanical Engineers (ASME) (www.asme.org)(a) Graphic Symbols for Plumbing, ANSI and ASA Y32.4(b) Graphic Symbols for Railroads Maps and Profiles, ANSI or ASA Y32.7(c) Graphic Symbols for Fluid Power Diagrams, ANSI or ASA Y32.10(d) Graphic Symbols for Process Flow, ANSI or ASA Y32.11(e) Graphic Symbols for Mechanical and Acoustical Elements as Used in Schematic Diagrams, ANSI or ASA Y32.18(f) Graphic Symbols for Pipe Fittings, Valves and Piping, ANSI or ASA Z32.2.3(g) Graphic Symbols for Heating, Ventilating and Air Conditioning, ANSI or ASA Z32.2.4(h) Graphic Symbols for Heat–Power Apparatus, ANSI or ASA Z32.2.6

4 4. Instrument Society of America (ISA) (www.isa.org)(a) Instrumentation Symbols and Identification, ISA-S5.1.

5 5. American Petroleum Institute (API) (www.api.org)

6 6. British Standards Institute (www.bsi-global.com)

Other symbols are established for specialized purposes. The physical equipment symbols established in some of these standards are often not as descriptive as those in the chemical, petrochemical, and petroleum industry is accustomed to using. The bare symbolic outlines given in some of the standards do not adequately illustrate the detail needed to make them useful. Accordingly, many process engineers develop additional detail to include on flowsheets, such as Figures 14.16a–e and 14.17a–c, which enhance the detail in many of these standards. Various types of processing suggest unique, yet understandable symbols, which do not fit the generalized forms.

Many symbols are pictorial which is helpful in representing process as well as control and mechanical operations. In general, experience indicates that the better the representation including relative location of connections, key controls and even utility connections, and service systems, the more useful will be the flowsheets for detailed project engineering and plant design.

To aid in readability by plant management as well as engineering and operating personnel, it is important that a set of symbols be developed as somewhat standard for a particular plant or company. Of course, these can be improved and modified with time and as needed, but with the basic forms and letters established, the sheets can be quite valuable. Many companies consider their flowsheets quite confidential since they contain the majority of key processing information, even if in summary form.

Figure 14.16 (a) Process variables; (b) Pumps and solids [9]. (c) Storage and equipment; (d) Flow and instruments [9]. (e) Filters, evaporators, and driers [9].