Q5-4 Heat Exchanger Simulation for Startup

J. W. Palen

Heat exchanger design calculations usually include additional specified resistances—or fouling factors—to account for possible deposit formation on the tubes. In some cases, fouling factors can be a realistic means of extending on-stream time before cleaning, but in many other cases, they are simply safety factors. In either case, the heat exchanger is usually clean at startup and performs as though the fouling resistances were zero. Thus, startup performance can differ dramatically from design performance. Too often designers/operators overlook this fact, which can result in operational problems. This article reviews a simulated start-up for three cases—a reboiler, a condenser, and a single phase heat exchanger. Startup performance is simulated using HTRI’s state-of-the-art software, IST.