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Module 5: Flowcharts and Ventilation Systems - Flowcharts - Symbols
IntroductionFlowchart Symbols
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Material Streams
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Major Components of Systems
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Minor Components of Systems
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Instruments
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Materials of Construction
Objective
- To identify the meaning of flowchart symbols used in air pollution control.
Flowcharts are a useful tool when you want to evaluate the performance of an entire system because they provide a means for organizing and presenting operating data. More specifically, flowcharts can be used for the following purposes:
- Evaluating process operating changes that are affecting control device performance
- Identifying instruments that are not working properly
- Identifying health and safety problems
- Communicating effectively
As discussed later (see lesson on Flowchart Diagrams) an expanded block diagram flowchart has been adopted for use in these modules. Major components such as baghouses are shown as a simple block rather than a complex sketch resembling the actual baghouse. A set of conventional instrument symbols and major equipment symbols have been adopted primarily from conventional chemical engineering practice.
Most of the standard symbols are reproduced on the back of the flowchart sheet so that you do not need to remember what they stand for. The form is basically "self contained."
A complete flowchart consists of several symbols representing major and minor pieces of equipment and numerous material flow streams. It is important to be able to differentiate between the various types of material flow streams without sacrificing simplicity and clarity.
The recommended symbols selected for the material streams are presented in Figure 1 
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Gas flow streams are shown as two parallel lines spaced slightly apart and therefore appear larger than other streams. This size difference is important so that the inspector can quickly scan the flowchart and differentiate between gas and liquid material flow streams. Segments of ductwork connecting one major piece of equipment to another are labeled with an alphabetic character.
Important liquid and solid material flow streams are shown as solid, single lines. Diamonds with enclosed numbers are used to identify each of the streams.
To avoid cluttering the drawing, some of the liquid and solid material streams for which operating data will not be necessary are unnumbered. These types of streams are often called utility streams for a couple of reasons. They provide necessary materials to the system being shown and the characteristics of these streams are relatively constant. Typical utility streams for air pollution control equipment systems include make-up water, cooling water, and low-pressure steam. Natural gas, oil, and other fossil fuels can also be treated as utility streams to simplify the drawings. Instead of the numbered diamonds, these utility streams are identified either by using one of the codes listed in Table 1 or by a one- or two-word title. The codes or work titles are placed next to a "stretched S" symbol, which is used to indicate that the source of the utility stream is outside the scope of the drawing.
A square or rectangle is used to denote major equipment such as the air pollution control devices, tanks and vessels, or process equipment. Fans are denoted using a relatively large circle with a set of tangential lines to indicate the discharge point. A stack is shown as a slightly tapered rectangle. All of these symbols are shaded or filled with crosshatched diagonal lines so that it is easy to pick out the major equipment items from the gas handling ductwork and other streams leaving these units (see Figure 2) 
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The items treated as major equipment depend on the overall complexity of the system being drawn and on individual preferences. These decisions are determined based primarily on the types of data and observations that are possible and the level of detail that is necessary to evaluate the performance of the overall system.
The stack (or emission discharge point) is obviously important due to the visible emission observations and the presence of continuous emission monitors and stack sampling ports in some systems. The emission points, which should be subject to Method 9 or Method 22 visible emission observations, are identified by a set of inverted triangles immediately above the source as shown in Figure 3. 
These are numbered whenever there is any possibility of confusing different sources within a single industrial complex. The numbers used in the triangles should correspond with the emission point identification numbers used in the inspector's working files. Typical identification numbers E1, E2, ... En are used for enclosed emission points such as stacks and F1, F2... Fn are used for fugitive emission points such as storage piles and material handling operations.
A number of relatively small components in air pollution control systems should be shown on the block-diagram-type flowcharts in order to clarify how the system operates. A partial list of these minor equipment components is provided in Table 2.
Symbols for the minor components listed in Table 2 are shown in Figure 4. 
Those used most frequently are also reproduced on the back of the flowchart form. Note that all of these symbols are relatively simple and quick to draw.
The presence of an instrument or a sampling port is indicated by a small circle connected to a stream line by a short dashed line as shown in the Figure below.
The type of instrument is indicated using the symbols listed in Table 3.
Instruments such as manometers and dial-type thermometers can only be read at the gauge itself. These indicating gauges, shown in Figure 5, are simply denoted by the instrument circle and the instrument code. More sophisticated instruments with panel-mounted readout gauges (normally in the control room) are indicated using a line horizontally bisecting the instrument circle. In this case, the instrument code is placed directly above the line. When the instrument readout is a continuous strip chart recorder or data acquisition system, the letter "R" for "Recording" is placed below the line.
The materials of construction are relevant whenever there has been or may be a serious corrosion problem that could affect either system performance or safety. On a single-page-format-type of flowchart, it is impractical to specify the exact types of material and protective coatings on each vulnerable component because there are several hundred combinations of materials and coatings in common use. However, the general type of material in certain selected portions of the system may be important. For example, it would be helpful to know that a stack discharging high concentrations of sulfuric acid vapor is composed of carbon steel because this material is easily attacked by sulfuric acid. The stack platform and access ladders could be vulnerable to failure as the corrosion problem gets progressively worse. A small set of symbols is presented in Table 4 for identifying materials of construction.
These symbols should be placed next to the major equipment item (e.g. stack, fan, and air pollution control device) or the gas handling ductwork segment.
Practice Problems
Flowcharts - Symbols
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Instructions:
- Complete the Practice Problems before proceeding to the next section. Click on the button below.