This example illustrates how the techniques used in an operability study can be used to decide the instrumentation required for safe operation. Figure 9.6a shows the basic instrumentation and control systems required for the steady-state operation of the reactor section of the nitric acid process introduced in Figure 4.2. Figure 9.6b shows the additional instrumentation and safety trips added after making the operability study set out below. The instrument symbols used are explained in Chapter 5.

 That this is a simplified flow diagram and a HAZOP based on the full P and I diagram would go into considerably more detail.

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M NH3 from storage (a) FIGURE 9.6(A) Air 101 Filter LV 103 Compressor NRV2 LIC 102 PIC Vaporizer FV 104 FT FFC 1 T FIC FT 1 FFV PV 1 109 Steam 105 PAL To scrubber TI 1 106 TI Reactor 107 AG