Process diagrams flow sheets

The first step is to have a complete and detailed description of the system, process, or procedure under consideration. This must include physical properties of the materials, operating temperatures and pressures, detailed flow sheets, instmment diagrams of the process, materials of constmction, other detailed design specifications, and so forth. The more detailed and up-to-date this information is, the better the result of the analysis. 

The first step in the procedure is to define the purpose, objectives, and scope of the study. The more precisely this is done, the more focused and relevant the committee discussions can be. The next step is to collect all relevant information on the process under consideration. This includes flow diagrams, process equipment specifications, nominal flows, etc. The procedure is highly dependent on the reflabiUty of this information. Efforts expended here are worthwhile. Many committees use the flow sheet as the central stmcture to organize thek discussions. 

Most flow sheets have one or mote recycles, and trial-and-ettot becomes necessary for the calculation of material and energy balances. The calculations in a block sequential simulator ate repeated in this trial-and-ettot process. In the language of numerical analysis, this is known as convergence of the calculations. There ate mathematical techniques for speeding up this trial-and-ettot process, and special hypothetical calculation units called convergence, or recycle, units ate used in calculation flow diagrams that invoke special calculation routines. 

Fig. 2. Process flow diagram for sheet-steel enameling where COM iadicates clean-only metal and PM, pickled metal, for (a) enamel preparation and...

The next step is to connect the individual unit operations in a block diagram, creating a process flow sheet. Figure 1 is an example of a simplified process flow diagram for a pattem-etch process for a printed wiring-board operation. There are... 

Step 5.4 Record Information on Process Flow Sheets. The input data collected for the material balance can be recorded on the process flow diagram, and in tabular form on a spreadsheet. 

DIN 28004 (1988) Flow sheets and diagrams of process plants, 4 parts (BSI). 

The P and I diagram will resemble the process flow-sheet, but the process information is not shown. The same equipment identification numbers should be used on both diagrams. 

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. 

A brief outline of the technique is given in this section to illustrate its use in process design. It can be used to make a preliminary examination of the design at the flow-sheet stage and for a detailed study at a later stage, when a full process description, final flow-sheets, P and I diagrams, and equipment details are available. 

HAZOP studies may be made on batch as well as continuous processes. For a continuous process, the working document is usually a set of flow sheets or piping and instrument diagrams (P IDs). Batch processes have another dimension time. Time is usually not significant with a continuous process that is operating smoothly, although start-up and shutdown must also be considered, when the continuous process will resemble a batch process. For batch processes, the working documents consist not only of the flow sheets or P IDs but also... 

Fig. 3.94. Process and instrument flow sheet diagram PI, P2 pumps Wl, heat exchanger Bl, B2, glass reactors FI, F2, membrane cells B3, B4 safety PTFE cells F3, F4, HPLC filter frits. Reprinted with permission from A. Rehorek et al. [155].

The nomenclature used in solvent extraction has been defined in Chapter 1 and is illustrated in Fig. 8.1. Not all of the steps shown in this figure will be found in every extraction process, but equally there may be occasions where it is necessary to add additional steps for example, to recover the extractant from the scrub raffinate. So while Fig. 8.1 is not a completely general flow diagram it covers most of the processes likely to be found in practice. Variations of this flow sheet will become apparent during the remaining chapters. 

A block diagram of the Monsanto process for acetic acid production is shown in Fig. 4.13. The process flow sheet is simple since the reaction conditions are mild (180°C/30-40 bar) when compared to the BASF process (250°C/700 bar). More than 40% of world s acetic acid is made by the Monsanto process. One of the problems with this process is the continuous loss of iodine. A block diagram of the Eastman process for acetic anhydride production is shown in Fig. 4.14. The process generates minimum waste, and all process tars are destroyed to recover iodine and rhodium. 

Example 4 Computational order for styrene process. A styrene process flow diagram is shown in Fig. 4-5. From this flow sheet it is apparent that there are two recycle streams in this simple process the unreacted ethylberizene is recycled and mixed with the fresh feed and the reactor effluent is recycled back to the heat exchanger. 

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