Symbols, process flow diagrams

Graphical Symbols for Process Flow Diagrams, ASA Y32.ll.1961, American Society of Mechanical Engineers, New York. 

Block flow diagrams are frequently used to represent chemical processes. These diagrams indicate by blocks the key processing steps of chemical reaction and separation. Considerably more detail is shown in process flow diagrams, which also include the auxiliary operations and utilize symbols that depict the type of equipment employed. 

Table 1.1 is a list of the commonly used continuous separation operations based on interphase mass transfer. Symbols for the operations that are suitable for process flow diagrams are included in the table. Entering and exit vapor and liquid and/or solid phases are designated by V, L, and S, respectively. Design procedures have become fairly well standardized for the operations marked by the superscript letter a in Table 1.1. These are now described qualitatively, and they are treated in considerable detail in subsequent chapters of this book. Batchwise versions of these operations are considered only briefly.

Figure 4.6 (a) Three large-scale PFRs and (b) the symbol used commonly to represent a PFR in process flow diagrams. 

ANSI, "Graphical Symbols for Process Flow Diagrams ", ANSI Y32.I I, 2003. 

SAA, "Graphical Symbols For Process Flow Diagrams For The Food Industry ", SAA AS 1109. 

Whatever type of compressor is being used, the symbol used in process flow diagrams is as shown in Fignre 9.3. 

Figure 1.4 Symbols for Drawing Process Flow Diagrams...

Process simulation software typically will produce a flowsheet, but this is probably not a true process flow diagram and should not be used as one in a report. There are two reasons for this. First, the simulator-produced flowsheet is unlikely to follow all the conventions of PFDs given in Chapter 1 regarding equipment symbols, line crosses, labels, and so on. Second, the process simulated is not the true process. One unit in the process simulator (such as a distillation column) maybe several pieces of equipment (tower, condenser, condensate tank, etc.) that need to be shown on a PFD. It is common to simulate a sin e unit (such as a process-process heat exchanger) as two units to decouple the recycle calculations. Some units, such as a storage tank, require no calculations in the process simulator and thus are not shown on its flowsheet. However, the simulator flowsheet is essential in the appendix of the report if the simulator report is included. Care should be taken to use the same stream numbers in the simulation flowsheet as in the PFD whenever possible. 

Y32.11-196KR1998) Graphic Symbols for Process Flow Diagrams in Petrolenm and Chemical Indnstries Order No. K00040 29.00... 

The symbols used to show the equipment, valves, instruments and control loops will depend on the practice of the particular design office. The equipment symbols are usually more detailed than those used for the process flow-sheet. A typical example of a P and I diagram is shown in Figure 5.25. 

DFDs are drawn with just four symbols data sources and sinks, processes, data flows and data stores (see Figure 5). Data sources are entities that provide data to the system (a source) or receive information from the system (a sink). These sources lie outside the boundary of the system and are not active participants in the processing that occurs within the system. A process is any activity that converts data into information. Generally, processes are named with a verb of the action in the process and are numbered at the top of the symbol. Numbers are useful for cross-referencing processes on lower-level diagrams to the activities in higher-level diagrams. Processes are interconnected with other processes by data flows. Data flows are symbols that represent data in motion. Each data flow is named with a noun that describes the data represented in the flow. A data flow must be attached to a process at some point, either as a source or as a sink. A data store is a representation of the data at rest. Examples of data stores could include electronic data files, a database table, or a physical file folder. 

Planning The scope of the process (beginning and end) must be defined. The developers of the flow diagram must agree on the use of symbols and the level of detail needed. These choices win be guided by the purpose of the flowchart. 

A wide choice of conventions is available for drawing flow diagrams, based on control system theory, cybernetics, and information theory. The best conventions seem to be the simplest, in which one symbol designates an input or output, another an intervention, and a third a process. The same symbols are used throughout both the model and its constituent submodels. 

To understand the design and function of a chemical plant it is a useful preliminary to study the flow diagram (sometimes called a flow sheet). Its purpose is to illustrate diagrammatically, on one sheet of paper, all the items of equipment required for a chemical process or series of processes to be operated. Items are represented by simple symbols which are usually those recommended by the British Standard 974 1953 and subsequent editions (your supervisor may have a copy). The route of materials through the equipment is indicated by arrows and interconnecting lines and, in some instances, the materials of construction, size or capacity, flow rates, power requirements, and pipe dimensions are also shown. 

It is important that the information contained in a PFD be clear and understandable to all who will need it, so the PFD should be drawn up in conformance with international standards. The most widely used standard is ISO 10628 Flow diagrams for process plants - General rules. Some of the most commonly used symbols are depicted in Fig. 3.11. 

Flow diagram—a simplified diagram that uses process symbols to describe the primary flow... 

Symbols and diagrams have been developed for most pieces of industrial equipment, process flows, and instrumentation. The symbols covered in this chapter include those typically used with valves, piping, tanks, pumps, compressors, steam turbines, motors, heat exchangers, cooling towers, furnaces, boilers, distillation columns, and reactors. Figure 7-6 shows many of the basic symbols for valves. 

On a typical flow diagram, distillation columns, reactors, boilers, and furnaces are drawn as they visually appear in the plant. If a proprietary process includes several types of equipment not typically found on a standard symbol file, the designer will draw the device as it visually appears in the unit. 

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