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Comment PDF Separation Processes

Facts at your Fingertips: Distillation

By Scott Jenkins |

Computer-generated simulations of distillation processes are often validated experimentally. This reference discusses three concepts that influence comparisons between experimental results and simulation predictions: vapor-liquid equilibrium (VLE) of the components; relative liquid-to-vapor flowrates (L/V ratios in the column); and vapor-liquid contactor (tray) efficiency. Understanding these concepts can help explain discrepancies between experimental data and simulation results. Vapor-liquid equilibrium The relative volatility of an ideal binary chemical system is equal to the ratio of the two pure-component vapor pressures. If the components’ interactions are close to ideal and the components have sufficient relative volatility (>2), then small errors in VLE predictions may not significantly affect the separation. However, if the relative volatility is small (<1.5), deviations between predicted and actual VLE will lead to large differences between the actual and predicted number of stages required to accomplish the separation. Non-ideal systems often have a pinch at the upper or lower end of the binary VLE curve (vapor and liquid compositions of both components are nearly equal). The pinch is usually at the upper (right-hand)…
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