Minimum Reflux (Underwood)
Estimate the minimum reflux ratio of a binary distillation by Underwood's equation (saturated-liquid feed), Rmin = [xD/xF − α·(1−xD)/(1−xF)]/(α − 1), from the relative volatility (α) and the light-component mole fractions in the distillate (xD) and feed (xF). At minimum reflux, the column would need infinite plates; the operating reflux is a multiple of it (1.1–1.5×). It is a key number in column design. Enter α, xD and xF.
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Refluxo mínimo (Underwood)
Toda coluna de destilação recircula parte do produto de topo de volta para a coluna — o refluxo — para melhorar a separação. Há um limite inferior: o refluxo mínimo (Rmin), abaixo do qual a separação desejada é impossível, nem com infinitos pratos. A equação de Underwood (aqui na forma para alimentação líquida saturada e mistura binária) estima esse mínimo a partir da volatilidade relativa α (o quão diferentes são as volatilidades dos dois componentes) e das frações molares do componente leve no destilado (xD, alta pureza desejada) e na alimentação (xF). No refluxo mínimo, formam-se zonas de composição constante (pinch) que exigem pratos infinitos. O refluxo de operação é sempre um múltiplo do mínimo (tipicamente 1,1 a 1,5·Rmin), num compromisso entre número de pratos e gasto de energia. Junto com o número mínimo de pratos (de Fenske), o Rmin de Underwood é a base do método Fenske-Underwood-Gilliland de projeto de colunas. Informe α, xD e xF.
Related Tools
Optimum Reflux Ratio
Compute a distillation column's operating reflux ratio, R = factor · Rmin, multiplying the minimum reflux by a factor (typically 1.1 to 1.5). There is a classic economic trade-off: a low reflux (near minimum) requires many plates (more column investment); a high reflux requires fewer plates but much more energy in the reboiler and condenser (more operating cost). The optimum balances the two. Enter the minimum reflux and the factor.
Actual Plates (Efficiency)
Compute the number of actual plates of a distillation column, N_actual = N_theoretical / (efficiency/100), from the number of theoretical (equilibrium) plates and the column's overall efficiency (%). Since no real plate reaches perfect equilibrium, more actual plates than theoretical are needed: a 50% efficiency doubles the plate count. It is the step that turns the theoretical design into the physical column. Enter the theoretical plates and the overall efficiency.
Number of Transfer Units (NTU)
Compute the number of transfer units (NTU) of an absorption or stripping column (dilute case), NTU = ln(C_in/C_out), from the inlet and outlet concentrations. NTU measures the 'difficulty' of the separation: the greater the removal desired, the more transfer units are needed. Together with the height of a unit (HTU), it defines the total packing height. Enter the inlet and outlet concentrations.
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