Page 29 - Applied Process Design for Chemical and Petrochemical Plants Volume I

Process Planning, Scheduling and Flowsheet Design 17

use of equipment summary tables similar to flow and pipe chemical, petrochemical, and petroleum industry is
data tables can avoid this objection and yet keep the infor- accustomed to using. The bare symbolic outlines given in
mation on the sheets. Some flowsheets include relief valve some of the standards do not adequately illustrate the
set pressures adjacent to the valves, volume capacities of detail needed to make them useful. Accordingly, many
storage tanks, etc. process engineers develop additional detail to include on
flowsheets, such as Figures 1-19 A-E and 1-20 A-€3-C which
Computer-Aided Flowsheet Design/Drafting enhance the detail in many of these standards. Various
types of processing suggest unique, yet understandable,
Current technology allows the use of computer pro- symbols, which do not fit the generalized forms.
grams and data bases to construct an accurate and Many symbols are pictorial which is helpful in repre-
detailed flowsheet. This may be a process type diagram or senting process as well as control and mechanical opera-
a piping and mechanical/instrument diagram, depend- tions. In general, experience indicates that the better the
ing on the input. See Figures 1-9, 1-10, 1-18A and 1-18B. representation including relative locating of connections,
key controls and even utility connections, and service sys-
Flowsheet Symbols tems, the more useful will be the flowsheets for detailed
project engineering and plant design.
To reduce detailed written descriptions on flowsheets, To aid in readability by plant management as well as
it is usual practice to develop or adopt a set of symbols engineering and operating personnel, it is important that
and codes which suit the purpose. Flowsheet symbol stan- a set of symbols be developed as somewhat standard for a
dardization has been developed by various professional particular plant or company. Of course, these can be
and technical organizations for their particular fields. improved and modified with time and as needed, but with
Most of these have also been adopted by the American the basic forms and letters established, the sheets can be
National Standards Institute (ANSI). The following sym- quite valuable. Many companies consider their flowsheets
bol references are related and useful for many chemical quite confidential since they contain the majority of key
and mechanical processes:
processing information, even if in summary form.
1. American Institute of Chemical Engineers Line Symbols and Designations
(a) Letter Symbols for Chemical Engineering, ANSI
Y10.12 The two types of lines on a flowsheet are (1) those rep-
2. American Society of Mechanical Engineers resenting outlines and details of equipment, instruments,
(a) Graphic Symbols for Plumbing, ANSI or ASA etc., and (2) those representing pipe carrying process or
Y32.4 utility liquids, solids, or vapors and electrical or instru-
(b) Graphic Symbols for Railroad Maps and Profiles, ment connections. The latter must be distinguished
ANSI or MA Y32.7 among themselves as suggested by Figure 1-21.
(c) Graphic Symbols for Fluid Power Diagrams, In order to represent the basic type of solution flowing
ANSI or ASAY32.10 in a line, designations or codes to assign to the lines can
(d) Graphic Symbols for Process Flow, ANSI or ASA be developed for each process. Some typical codes are:
Y32.11
(e) Graphic Symbols for Mechanical and Acoustical RW - River Water
Elements as Used in Schematic Diagrams, ANSI TW - Treated Water
or ASAY32.18
SW - Sea Water
(f) Graphic Symbols for Pipe Fittings, Valves and Pip- BW - Brackish Water
ing, ANSI or ASA 232.2.3
(9) Graphic Symbols for Heating, Ventilating and Air CW - Chilled Water
Conditioning, ANSI or MA 232.2.4 S - Low Pressure Steam
(h) Graphic Symbols for Heat-Power Apparatus, S150 - 150 psi Steam
ANSI or ASA 232.2.6 S400 - 400 psi Steam
3. Instrument Society of America V - Vent or Vacuum
(a) Instrumentation Symbols and Identification, ISA- C - Condensate (pressure may be indicated)
S5.1, also see Reference 27 D -Drain to sewer or pit
EX - Exhaust
Other symbols are established for specialized purposes. M - Methane
The physical equipment symbols established in some of A - Air (or PA for Plant Air)
these standards are often not as descriptive as those the F - Freon